m  MEMOI 

Richard  M. 

RIAM 
Holman 

,  

«OLOGY 


Richard  *V,  Holman 


A  COMPENDIUM 


OF 


GENERAL    BOTANY. 


BY 

DR.  MAX  WESTERMAIER, 

Professor  in  the  Royal  Lyceum,  Freising,  Germany. 
TRANSLATED  BY 

DR     ALBERT  SCHNEIDER, 

Fellow  in  Botany,  Columbia  College,  New  York. 


171  UUustratfons. 


FIRST  EDITION. 

FIRST  THOUSAND. 


NEW  YORK : 

JOHN    WILEY    &    SONS. 

LONDON:   CHAPMAN  &  HALL,  LIMITED. 

ST.  LOUIS   (17  S.  Broadway):    B,    HERDER, 

1896. 


BIOLOGY 

LIBRARf 

G 


Copyright,  1898, 

BY 
ALBERT  SCHNEIDER 


ROBERT   DRUMMOND,    ELECTROTYPER  AND   PRINTER,   NEW  YORK. 


PREFACE. 


IN  a  compendium  of  botany  intended  for  high  schools  it  is 
permissible  to  introduce  subject-matter  which  would  be  objec- 
tionable in  a  text-book  of  elementary  instruction.  Free  use  has 
been  made  of  such  privileges.  It  is  assumed  that  the  pupil  has  a 
general  knowledge  of  chemistry,  of  physics,  of  the  proper  use 
of  scientific  terminology,  and  has  the  ability  to  estimate  the 
value  of  hypotheses  and  undecided  problems.  From  the  con- 
sideration of  the  latter  the  disciple  of  our  science  will  soon 
recognize  the  peculiar  difference  between  layman  and  scientist. 
The  layman  looks  upon  many  phenomena  in  plant-life  as  being 
quite  clear  and  easy  of  explanation.  The  scientist,  however, 
can  demonstrate  that  we  know  but  very  little  concerning  these 
same  phenomena.  It  must  also  be  borne  in  mind  that  scientific 
progress  depends  upon  the  recognition  of  the  present  limits  of 
our  knowledge. 

Nearly  every  branch  of  science  is  more  or  less  merged  into 
general  cosmology.  It  is  therefore  expected  that  every  scientist 
should  attempt  to  explain  this  relation.  We  find  that  the  vari- 
ous authors  have  a  tendency  to  call  the  reader's  attention  to  the 
important  (in  the  author's  opinion)  phases  of  cosmological  rela- 
tionship. Even  of  this  privilege  I  have  made  use. 

Incidentally  I  will  make  the  following  observation :  The 
greater  portion  of  physiology  is  intimately  associated  with 
anatomy.  In  accordance  with  this  we  find  that  the  newer  devel- 
opment of  botanic rJ  science  considers  the  question,  What  for  ? 
of  prime  importance  when  investigating  plant-structures  (ana- 
tomical-physiological tendency  of  Schwendener's  school). 

In  the  special  as  well  as  in  the  general  treatment  of  the 
subject-matter  I  have  frequently  made  use  of  the  works  of 
NAGELI,  SACHS,  PFEFFEK,  DE  BARY,  FRANK,  GOBEL,  and  WARMING  ; 
more  especially  those  of  SCHWENDENER  and  his  pupils  (Haber- 
landt  among  others).  To  this  I  have  added  the  knowledge 

iii 

921916 


IV  PREFACE. 

obtained  through  a  long  scientific  association  with  my  honored 
instructor,  Professor  Schwendener.  The  illustrations  are  added 
with  the  kind  permission  of  various  authors.  For  all  this  I 
express  my  sincerest  gratitude. 

MAX  WESTEBMAIEK. 
FREIPING,  October  1893. 


TRANSLATOR'S  PREFACE. 


IN  presenting  this  translation  it  is  perhaps  well  to  offer  a  few 
explanatory  statements. 

The  book  is  just  what  the  title  implies,  a  compendium  of  gen- 
eral botany.  Its  great  value  as  a  text-book  lies  in  the  thoroughly 
logical  and  scientific  treatment  of  the  subject-matter.  The  neces- 
sarily condensed  retrospect  of  the  science  of  botany  is  well 
supplemented  by  the  copious,  well-chosen  references  to  standard 
authorities. 

I  have  endeavored  throughout  to  adhere  as  closely  as  possible 
to  the  author's  form,  style,  and  concept  of  the  science  of  botany. 
The  arrangement  and  treatment  of  the  subject-matter  are  the 
same  as  in  the  original.  In  fact  I  have  endeavored  to  make  it  a 
translation  in  the  true  sense  of  the  word.  I  have,  however, 
added  some  foot-notes.  A  few  are  explanatory  ;  others  serve  to 
indicate  differences  of  opinion.  Although  it  is  difficult  to  make 
a  good  translation  of  the  finer  shades  of  meaning  peculiar  to 
a  language,  yet  I  sincerely  hope  I  have  met  with  fair  success  in 
such  an  attempt. 

Finally,  I  desire  to  express  my  grateful  obligations  to  Dr. 
N.  L.  Britton,  who  made  the  final  corrections  of  the  proof  for 
the  first  half  of  the  translation.  I  am  also  greatly  indebted  to 
my  wife,  who  has  kindly  aided  me  in  correcting  the  manuscript 
and  in  reading  the  proof. 

ALBERT  SCHNEIDER. 
COLUMBIA  COLLEGE,  July  1895. 


TABLE  OF  CONTENTS. 


PAGE 

PREFACE .       .  iii 

TRANSLATOR'S  PREFACE v 

Divisions  of  Scientific  Botany  and  General  Considerations     .       .  1 

PART  I. 

The  Cell. 

I.  Introduction 4 

II.  Primordial  Utricle  and  Cell  wall  in  Their  Mutual  Relation- 

ship.    Turgor.    Plasmolysis       ..       .        ..       ....  7 

III.  Cell-contents     .       .        .        .       .        ...       .        .       .  10 

A.  Living  Inclusions  of  the  Cytoplasm       ...        .        .        .  10 

(a)  Nucleus 10 

(b)  Chlorophyll-grains,  Chromoplastids,  Leucoplastids  ...  13 

B.  Dead  Inclusions  of  Cytoplasm        .        .        .        .        ...  16 

(a)  Starch        .        .        .        .        ...  '  .        .        ...        .  17 

(b)  Aleuron-grains  . 21 

(c)  The  Remaining  Solid  Dead  Inclusions  of  the  Cell  .        .        .22 

C.  The  Cell-sap  and  the  Remaining  Fluid  Contents  of  the  Cell         .  24 
IV.  The  Cell-wall .25 

A.  Internal  Structure  and  Method  of  Growth  of  the  Cell- wall          .  26 

B.  Chemical  Composition  and  Subsequent  Changes  in  the  Cell-wall  30 

C.  Products  of  the  Growth  in  Thickness  and  Surface  of  the  Cell- 

walls    .        .        .        .        ...        .        ,        .        .        .  32 

V.  The  Origin  of  Cells         .        ...       .               ...  42 

PART  II. 

Tissues  and  Simple  Organs. 

A.  Structure  of  Tissues  and  Simple  Organs 45 

B.  Differentiation  of  Tissues  according  to  Structure  and  Func- 

tion (Physiological  Anatomy  of  Simple  Organs)     ...  49 

Differences  of  Functions  and  Their  Enumeration    ....  49 

SPECIAL  FUNCTIONS  : 

I.  The  Function  of  Formative  Tissues  (Meristem  and  Cambium)     .  51 

II.  Structure  and  Function  of  the  Epidermal  Tissue-system     .        .  53 

III.  Function  of  Mechanical  Tissues 63 

vii 


Vlll  TABLE  OF  CONTENTS, 

PAGE 

IV.  The  Function  of  the  Conducting  System 70 

Consideration  of  the  Conducting   System  in  Itself  and  in  Its 

Relation  to  the  Mechanical  System  ......  70 

(a)  The  Various  Cell-forms 70 

(b)  The  Laticiferous  Tissue 76 

(c)  The  Stem-structure  of  Mosses  and  Vascular  Cryptogams      .  78 

(d)  The  Stem  of  Monocotyledons,  Dicotyledons,  and  Gymno- 

sperms         ..........  80 

(e)  Growth  in  Thickness  among  Dicotyledons  and  Monocoty- 

ledons by  Means  of  the  Cambium 87 

(/)  Abnormal  Structure  of  Stems 94 

(g)  The  Structure  of  Roots 95 

(h)  Anatomy  of  the   Transition-zone  between  the  Stem  and 

the  Root 98 

(0  The  Special  Physiology  of  the  Movements  of  Food-sub- 
stances and  Water  in  Plants        ......  99 

a.  Conduction  of  Albumen 99 

P.  Conduction  of  Carbohydrates 101 

y.  Conduction  of  Water 103 

Protective  Sheath  or  Endoderm.     (Concluding  Chapter  to  the 

Three  Foregoing  Ones  on  Special  Functions.)      ....  112 

V.  Protection  of  the  Meristematic  Areas  of  the  Plant-body    .        .  115 
(a)  The  Protection  for  the  Terminal  Meristematic  Areas  of  the 

Plant-body 115 

a.  Protection  of  the  Root-tip 115 

ft.  The  Protection  of  the  Stem-apex 118 

y.  Protection  of  the  Leaf -tip 119 

(b)  Protection  for  Areas  of  Intercalary  Growth  ....  119 
VI.  Food-substances  Derived  from  the  Atmosphere.     Assimilation 

of  Carbon  in  Green  Organs 122 

(a)  The  Structural  Principles  of  the  Assimilating  System  .        .  123 

(b)  Movements  and  Changes  in  Form  of  Chlorophyll-bodies      .  128 

(c)  The  Chemistry  and  Physiology  of  Chlorophyll      .        .        .  128 
VII.  The  Function  of  Aeration 132 

(a)  The  Structure  and  Function  of  Breathing-pores  (Stomata)  135 

(ft)  Lenticels 138 

VIII.  The  Function  of  Roots        .        .        .        .        .        .        .        .  139 

(a)  Subterranean  Roots        .         . 139 

(b)  Aerial  Roots 140 

IX.  The  Appropriation  of  Assimilated  Food-substances    .        .        .  141 

(a)  Condition  of  Seeds  before  the  Beginning  of  Assimilation     .  142 

(b)  Nutrition  of  Saprophytes  and  Parasites  .....  143 

(c)  Symbiosis        ..........  145 

(d)  Insectivorous  Plants .        .  148 

X.  The  Storing  and  Function  of  Reserve  Material  ...  150 

(a)  Storing  of  Water 150 

(ft)  The  Storing  of  Starch  and  Other  Food-substances,   Espe- 
cially the  Albuminous  Substances       .....  151 
XI.  Secretion  152 


TABLE  OF  CONTENTS.  ix 

PART  III. 
Organs  and  Systems  of  Organs. 

PAGE 

I.  The  Morphological  and  Physiological  Relations  of  Organs     .  155 

A.  The  Principal  Forms  of  Organs 155 

B.  Modification  of  Organs 157 

(a)  Modification  of  Stem  and  Root        .        .        .        .        .        .  157 

(b)  Modification  of  the  Phyllome 159 

Critical  Observations  on  the  Distinction  of  Organs  .        .        .  163 

C.  The  Complex  Organ  :  Shoot 165 

D.  Metamorphosis  and  Correlation 167 

II.  Origin  and  Position  of  Lateral  Organs  and  the  Causes  for 

Their  Definitive  Position 168 

A.  Spiral  Arrangement  of  Leaves.    Theories  of  Phyllotaxy      .        .  171 

B.  The  Determination  of  a  Divergence       ......  174 

C.  The  Mechanical  Theory  of  Phyllotaxy  and  the  Idealistic  Concep- 

tion of  Nature ...  175 

III.  Difference  in  the  Power  of  Development  of  the  Members  of 

Equal  Morphological  Value.  Classification  of  Organ-systems  179 

A.  Inflorescence  .         ... 181 

(a)  Racemose  Inflorescence    .        . 182 

(b)  Pauiculose  Inflorescence  . •  •  •-  > 182 

(0)  Cicinnose  Inflorescence      .                 182 

B.  Rank  and  Succession  of  Shoots  183 


PAKT  IV. 

Reproduction. 

Introduction 185 

I.  Reproduction  among  Cryptogams  .        ...       ....  188 

A.  Forms  of  Reproduction  among  Algae 192 

B.  Forms  of  Reproduction  among  Fungi 194 

II.  A   Comparative  Study  of  Reproduction  and  Alternation  of 

Generation  in  Mosses,  Vascular  Cryptogams,  and  Phanero- 
gams   200 

Gymnosperms  and  Angiosperms       .        .        .        .         .         .        .  210 

III.  The  Phanerogamic  Flower     .        .        .      V      ....  213 

A.  Calyx,  Corolla,  Nectaries.     The  Flower  as  a  Whole     ...        .  214 

B.  The  Stamens  and  Pollen-grains      .        .      .  .        ...        .  223 

C.  The  Gyncecium.     The  Ovule  with  the  Embryo-sac  before  and 

after  Fertilization        . 227 

IY.  The  Morphology  and  Physiology  of  the  Seed  and  Fruit  of 

Phanerogams                 *        » 231 

Germination      .     -  .        .        .        . 237 

V.  The  General  Physiology  of  Reproduction 238 

A.  Agents  in  Fertilization.     Cross-pollination.     Self-pollination       .  238 


X  TABLE  OF  CONTENTS. 

PAGE 

B.  Fertile  Seeds.     Hybridization.     Apogaray    .        .        .  241 

C.  Variability,  Constancy,  Heredity .  243 

D.  Special  Creation  and  the  So-called  Theory  of  Natural  Descent    .  244 
Appendix:  The  Life-period  of  Plants 250 


PART  Y. 

The  General  Chemistry  and  Physics  of  Plant-life. 

I.  Chemical  Physiology 252 

Selection 257 

The  Cyclic  Course  of  Food-substances 258 

II.  The  Physiology  of  Growth 253 

A.  Active  and  Passive  Growth 261 

B.  The  Results  of  Unequal  Growth 261 

(a)  Tissue-tension 262 

(V)  Curvatures 263 

(c)  Torsions 264 

C.  Molecular  Organization  of  Plant-structures 266 

III.  Temperature,  Light,  Gravity,  and  Other  Factors  in  Their  Re- 
lation to  Plant-life       268 

A.  Effects  of  Temperature 268 

(a)  Production  of  Warmth  and  Cold 268 

(b)  The  Effect  of  Temperature  upon  Plant-life      ....  269 

B.  Effect  of  Light 270 

(a)  Production  of  Light 270 

(b)  Influence  of  Light  upon  Plant-life 271 

C.  Influence  of  Gravity        .........  275 

D.  Electricity,  Moisture,  Water- currents,  Radiating  Heat         .        .  276 
IT.  The  Physiology  of  Plant-movements 277 

A.  Classification  of  Movements  according  to  Cause.     The  Outward 

Manifestation  of  Some  Movements 277 

B.  Hygroscopic  Movements         ........  278 

C.  Autonomous  Movements 279 

D.  Irritable  Movements 280 

Mimosa 280 

Behavior  of  Tendrils.     Conduction  of  Stimuli.     The  Function  of 

Irritable  Movements 281 

E.  The  Physiology  of  Twining 283 


PART  VI. 
Classification  of  Plants.    Taxonomy     .      .      286 

ALPHABETICAL  INDEX 293 


COMPENDIUM  OF  GENEEAL  BOTANY, 


DIVISIONS  OF  SCIENTIFIC  BOTANY  AND  GENEKAL 
CONSIDEEATIONS. 

THE  two  domains  of  plant  study  are  MOEPHOLOGY  and  PHYSI- 
OLOGY. 

Morphology  treats  of  the  substance  of  the  vegetable  kingdom. 
Physiology  treats  of  the  forces  or  energies  bound  up  with  the 
plant-substance  or  which  manifest  themselves  with  it.  Plant-func- 
tions, as  we  know  them  in  the  light  of  morphology  and  physiology, 
are  not  only  proper  adjustments  to  the  environment,  but  above  all 
fulfill  the  requirements  of  plant-life  and  are  therefore  life-func- 
tions. To  define  the  term  life,  even  only  in  its  application  to  the 
plant  kingdom,  is  impossible.  Science  can,  however,  proceed  more 
and  more  into  the  order  of  things,  to  know  more  clearly  the  prop- 
erties of  matter  and  the  harmonious  manifestations  of  force.  In 
spite  of  this  progress  we  cannot  approach  any  nearer  the  solution 
of  the  "  life-problem."  Processes  of  a  chemical  and  physical  nature 
are  the  most  that  we  are  able  to  see  in  this  order  of  things  and 
this  knowledge  distinguishes  the  scientist  from  the  layman  who  sees 
the  order  less  clearly.  The  earnest  investigator  who  has  concluded  to 
believe  by  faith  finds  the  answer  to  the  "why"  of  this  order  in  the 
words  "  wonder  of  creation."  To  the  one  who  is  not  so  inclined 
this  "why"  becomes  a  darkness  which  grows  denser  in  propor- 
tion as  he  sees  more  clearly  the  order  in  which  chemical  and 
physical  processes  are  combined  as  they  are  in  plant-life.  Life 
manifests  itself  in  certain  chemical  and  physical  processes,  and  in 
so  far  as  physics  and  chemistry  are  concerned  in  life-processes  there 
is  a  "  physics  and  chemistry  of  plant-life."  Plant-physiology  may 
be  designated  by  the  expression  "  physics  and  chemistry  of  plant- 


2  DIVISIONS  OF  SCIENTIFIC  BOTANY 

life,"  but  always  in  the  sense  that  the  exactness  of  the  knowledge 
of  life-manifestations  adds  nothing  to  the  causal  mechanical  expla- 
nation of  "life"  itself. 

To  morphology  in  the  above  sense  belongs  the  description  of  the 
form,  size,  arrangement,  and  outer  and  inner  numerical  relations  of 
the  plant-body ;  therefore  anatomy  is  a  part  of  morphology  in  the 
wider  sense.  Usually,  however,  anatomy  (inner  form-relations)  is 
distinguished  from  morphology  in  a  narrower  sense  (outer  form- 
relations).  Thus  limited,  morphology  forms  one  of  the  fundamental 
principles  underlying  our  present  system  of  classification. 

Let  us  now  return  to  the  two  main  divisions  of  our  science.  A 
few  examples  will  make  clear  to  the  novice  how  morphology  may 
be  distinguished  from  physiology,  but  that  a  complete  and  compre- 
hensive knowledge  of  the  plant  necessitates  a  combination  of  the  two. 

"When  an  investigation  has  for  its  purpose  the  explanation  of 
the  cause  of  development  of  the  woody  cell-wall,  then  it  concerns 
itself  with  a  function,  in  this  special  case  a  function  of  nutrition ; 
this  is  therefore  physiology.  If  one  makes  a  microscopic  compari- 
son of  one  wood  with  another  and  seeks  to  find  the  similarities  or 
dissimilarities  of  the  tissues,  then  no  functions  are  involved  and 
the  study  is  morphology  (anatomical  morphology).  If  one  seeks 
to  find  the  relation  of  anatomical  differences  to  the  environment 
(as  a  rule  this  relation  is  considered  from  a  teleological  stand- 
point), then  we  must  of  necessity  concern  ourselves  with  phys- 
iological processes.  If  we  seek  after  the  conditions  which  cause 
plants  to  turn  green,  then  the  study  is  purely  physiological :  we  are 
solely  concerned  with  energies.  If,  with  the  aid  of  the  highest 
magnifications,  the  finest  structure  of  chromoplastids  (chlorophyll 
bodies)  is  studied  in  order  to  describe  them  more  correctly,  we  are 
concerned  only  with  morphology.  Development,  for  example,  em- 
bryology, belongs  to  morphology.  To  study,  describe,  and  repre- 
sent graphically,  the  successive  stages  of  embryonic  development 
lies  wholly  in  the  domain  of  morphology.  If  one,  however,  makes 
a  study  of  the  wall  of  the  ovum  in  order  to  determine  experimen- 
tally what  forces  eventually  determine  the  position  of  the  first 
septum,  then  we  are  again  in  the  domain  of  physiology.  If  a 
minute  description  is  given  of  the  various  cell-forms  found  in  the 
stem,  where,  for  example,  the  thick-walled  cells  occur,  the  form 
of  the  thickenings,  etc.,  then  we  are  concerned  with  morphology. 
If,  however,  one  seeks  for  the  significance  of  this  or  that  cell- 


AND   GENERAL   CONSIDERATIONS.  3 

form  in  the  service  of  plant-life,  then  again  we  are  concerned  with 
a  force  effect  which  is  bound  to  a  specially  constituted  plant-sub- 
stance and  is  therefore  physiology. 

Throughout  the  arrangement  of  this  book  a  strong  effort 
is  made  to  adhere  as  strictly  as  possible  to  the  combination  of 
such  methods  of  investigation  as  have  just  been  indicated.  How- 
ever, some  attention  must  be  given  to  the  didactic  uses  of  the  book. 
Due  regard  shall  be  given  to  a  proper  summarizing.  In  its  entirety 
we  have  adopted  that  disposition  of  subject-matter  which  SCHWEN- 
DENEK  has  so  efficiently  tested  and  found  useful  in  the  academic 
course  of  study.  His  arrangement  is  as  follows : 
I.  The  cell. 

II.  Tissues. 

A.  Structure  of  tissues  and  simple  organs. 

B.  Differentiation  of  tissues  (physiological  anatomy  of 
simple  organs). 

III.  Systems  of  organs. 

IV.  Reproduction. 

V.  General  chemistry  and  physics  of  plant-life. 
VI.  System  of  plant  classification. 


PAET  I. 
THE    CELL 


I.  INTEODUCTIOK 

The  organisms  which  we  designate  as  plants,  though  variable, 
have  one  thing  in  common :  they  are  either  single  cells  or  cell- 
complexes.  There  is,  so  to  speak,  only  one  element  in  plants,  and 
that  is  the  cell.  Every  plant  consists  of  at  least  one  cell. 

Omitting  for  the  present  the  embryonic  conditions  of  the  cell,  it 
may  be  defined  as,  for  the  most  part,  a  microscopic  closed  vesicle 
consisting  of  wall  or  covering  and  contents  (large  cells,  as  those  of 
Gossypium  species,  6  cm.  long ;  medium-sized  cells,  as  those  of  elder- 
pith).  We  must  distinguish  between  younger  and  older  stages  of 
the  cell.  At  first  an  apparently  homogeneous,  mucous,  tenacious 
substance— plasm,  protoplasm — fills  the  entire  cell-cavity  (lumen] 
and  is  enclosed  by  the  cell-wall  (membrane].  The  components  of  the 
cell-contents  designated  by  the  collective  noun  "plasm"  are  albumi- 
noid substances  and  hence  contain  besides  carbon,  hydrogen,  oxygen, 
also  nitrogen,  sulphur,  and  sometimes  phosphorus.  Its  mucous  consist- 
ency is  noticeable  by  its  spontaneous  escape  from  openings  of  the  cell- 
wall  (swarm-spore  formation  of  algse,  etc.).  Gradually  there  appear 
differentiations  in  the  apparently  homogeneous  plasm.  Spherical 
particles  filled  with  a  watery  substance — vacuoles1 — are  distinguish- 
able from  the  more  dense  contents  ;  the  latter,  the  true  plasm,  are  of 
different  kinds,  not  homogeneous,  as  a  superficial  examination  would 
indicate.  Tlieplasmic  utricle,  which  is  of  special  importance,  shall 


1  According  to  more  recent  investigation  (WENT)  the  "vacuoles"  originate 
from  pre-existing  ones.  (The  conclusions  of  this  investigator  are  generally  con- 
ceded to  be  erroneous. — Trans.) 

4 


THE  CELL. 


first  claim  our  attention.  The  water-bearing  cavities  (vacuoles)  in- 
crease more  and  more  in  size  and  subsequently  come  in  contact  and 
become  flattened  by  mutual  pressure.  Finally  they  are  separated 
only  by  thin  plasmic  membranes  and  threads ;  when  these  break  the 
vacuoles  flow  together  to  form  one.  The  plasm  then  lines  the  inner 
surface  of  the  cell- wall  as  a 
membrane  which  is  usually 
very  thin,  but  which  is 
never  absent  from  the  liv- 
ing cell.  This  membrane 
is  called  the  primordial 
utricle  or  plasmic  utricle. 
On  account  of  its  frequently 
immeasurable  thinness  it  is 
invisible  as  long  as  it  is 
in  contact  with  the  cell- 
wall.  If  by  artificial  means 
the  plasmic  utricle  can  be 
caused  to  separate  from  the 
wall  by  contraction,  then 
this  is  looked  upon  as  giv- 
ing evidence  that  it  was  a 
living  cell.  (Compare  Fig. 

10 

The  cell-wall  and  the 
plasmic  utricle,  the  two 
coverings  of  the  cell  con- 
tents, differ  (1)  chemically, 
in  that  the  primordial  utri- 
cle being  a  part  of  the  plasm 
is  an  albuminoid  substance, 
while  the  cell-wall  belongs 
to  the  group  of  carbohy- 
drates and  contains  there- 
fore C,  H,  and  O,  the  latter 
in  the  proportion  to  form 
water  (H2O) ;  (2)  physically,  in  that  the  cell-wall  is  highly  elastic 
with  but  little  extensibility,  while  the  plasmic  utricle  is  very  ex- 
tensible and  only  slightly  elastic.  To  this  must  be  added  a  second 
physical  difference,  that  of  diosmosis.  The  physical  differences  are 


•fl 


'  —  *  oun£  parenchyma-cell  of  Zea  Mays. 
A  normal;  5,  plasmolyced.    m,  membrane;  p  and 
h<  protoplasmic  utricle;    n,    nucleus;    s,   cell-lumen 

witb  ^p.  (After  prank.) 


6  COMPENDIUM  OF  GENERAL  BOTANY. 

of  such  great  importance  that  they  will  be  more  fully  treated  in 
Chapter  II. 

The  formation  of  the  plasmic  utricle  is,  as  has  been  indicated, 
not  the  only  differentiation  product  of  the  plasm.  In  the  entire 
plasmic  body  one  can  distinguish  a  fundamental  substance  ("  cyto- 
plasm"— from  ^uros",  cavity,  cell)  and  inclusions  formed  within  this 
fundamental  substance.  These  inclusions  are  of  two  kinds,  (A) 
living  and  (B)  dead.  Tho  plasmic  utricle  and  threads  constitute 
the  cytoplasm.  The  living  inclusions  are  the  nucleus,  the  chromato- 
phores,  and  the  fertilizing  elements,  made  up  chiefly  of  nuclear  sub- 
stance and  having  a  reproductive  function.  Of  the  dead  substances 
formed  from  the  plasmic  body  the  most  important  are  protein- 
grains,  protein-crystals,  starch-grains,  crystals  (of  fat,  salts,  organic 
acids,  etc.),  oil-globules,  and  tannin.  The  term  "  chromatophores  " 
includes  three  substances:  chlorophyll  bodies,  color-granules,  and 
colorless  starch-builders.  These  bodies  are  considered  collectively 
because  they  are  either  the  bearers  of  color-substances  or  are  formed 
out  of  such  to  be  again  converted  into  chromoplastids.  (STRAS- 

BURGER,  SCHIMPER.) 

The  space  not  occupied  by  the  above-mentioned  solid  constitu- 
ents is  filled  with  a  watery  fluid,  the  cell-sap  (sometimes  having 
color-substances  in  solution). 

It  is  important  to  bear  in  mind  that  within  the  living  cell  gas 
accumulates  only  in  very  small  quantities.  No  bubbles  are  ever 
rapidly  formed. 

The  reaction  of  cytoplasm  is  usually  alkaline  or  neutral.  In  the 
living  cell,  cytoplasm  has  the  property  of  reducing  very  dilute  alka- 
line silver-nitrate  solutions.  (Low  and  BOKORNI.)  In  the  cytoplasm 
an  outer  hyaline  layer  (hyaloplasm)  and  a  more  granular  internal 
layer  (polioplasm)  may  be  noticed.  According  to  REINKE  the 
plasmodia  of  Aethelium  septicum  contain  73$  of  water,  and  judging 
from  the  mucous  nature  of  other  forms  of  cytoplasm  we  may  con- 
clude that  they  also  contain  a  high  percentage  of  water.  To  plasm 
in  general,  especially  its  important  structures,  as  nucleus  and  chloro- 
plastids,  one  no  longer  ascribes  homogeneity.1  Careful  microscopic 
examinations  reveal  a  reticulated  (spongy)  structure  of  plasm. 
(SCHMITZ,  BUTSCHLI,  and  others.) 

All  life-processes  of  the  cell  take  place  within  the  plasm.     A 


1  I  would  especially  recommend  WIESNER'S  Elementarstructur,  1892. — Trans. 


THE  CELL.  7 

cell  without  plasm  does  not  grow,  does  not  take  in  food,  does  not 
live.  There  is  no  mechanics  of  plasm  ;  cell-life  is  still  wrapt  in 
obscurity.  Direct  observation  shows  that  plasm  gives  rise  to 
the  cell-wall,  as  in  the  case  of  Stigeoclonium..1  The  plasmic  utricle 
contracts,  escapes  from  the  opening  in  the  cell-wall,  and  in  time 
surrounds  itself  with  a  new  wall.  To  trace  a  phenomenon  back  to- 
plasm  is  as  a  rule  the  present  limit  of  our  ability. 

II.  PRIMORDIAL  UTRICLE  AND  CELL- WALL 

IN      THEIR      MUTUAL     RELATIONSHIP. 

TURGOR.    PLASMOLYSIS. 

The  primordial  utricle  is  usually  of  immeasurable  thinness.  In 
order  to  represent  it  in  a  figure  such  cells  or  portions  of  cells  are 
selected  in  which  it  is  of  perceptible  thickness  as  it  lies  in  contact 
with  the  cell-wall.  As  a  rule  it  can  be  made  visible  only  by  caus- 
ing it  to  separate  from  the  cell-wall  either  through  causes  inherent 
in  the  cell  itself  or  by  artificial  means.  When  this  plasmic 
contraction  is  artificially  induced  it  is  recognized  as  "plasmoly- 
sis."  The  phenomenon  of  plasmolysis  can  be  explained  only  from 
the  inherently  different  properties  of  the  cell- wall  and  primordial 
utricle.  It  is  at  once  evident  that  the  endosmotic  properties  of  the 
bladder  of  an  animal  filled  with  a  solution  of  some  salt  cannot  be 
compared  with  a  living  cell.  It  can  only  be  compared  with  a  dead 
cell- wall. 

If  a  living  cell  with  cell-sap  (ex.,  hair-cell  of  petal  of  Tradescantia) 
of  a  given  concentration  is  placed  in  distilled  water,  then  the  endos- 
motic flow  of  water  through  cell-wall  and  primordial  utricle  into  the 
cell  is  greater  than  the  outflow  of  cell-fluid.  The  endosmotic  sub- 
stances within  the  cell  attract  the  water,  which  therefore  increases  the 
cell  volume.  The  limit  of  this  increase  is  determined  by  the  cell- 
wall  because  it  is  less  extensible  than  the  primordial  utricle,  although 
much  more  elastic.  (Elasticity  is  that  force  which  replaces  dis- 
placed molecules.  It  is  very  great  in  the  cell-wall  and  very  small  in 
the  plasmic  utricle.)  The  cell-wall  is  therefore  a  hindrance  to  the 
excessive  expansion  of  the  primordial  utricle.  Action  induces 
reaction :  the  cell-sap  which  exerts  a  given  pressure  upon  the  cell- 
wall  in  turn  receives  an  equal  pressure.  This  mutual  pressure 
of  cell-sap  upon  cell- wall  and  cell-wall  upon  cell-sap  is  called 


1  Studied  by  N  AGE  LI. 


8  COMPENDIUM  OF  GENERAL  BOTANY. 

"  Turgor"  l  Sometimes  the  cell-wall  cannot  resist  the  expansive 
force  of  the  continually  expanding  primordial  utricle,  and  as  a  result 
the  wall  will  rupture,  which  indeed  sometimes  happens  in  nature. 
If  the  utricle  is  not  ruptured  at  the  same  time,  then  it  may  expand 
to  the  limit  of  resistance  and  finally  rupture. 

Let  us  now  suppose  an  inverse  case.  Let  there  be  a  more  highly 
concentrated  solution  outside  and  a  relatively  more  dilute  cell-sap 
within  the  cell.  In  this  case  more  fluid  passes  outward,  and  as  a 
result  the  entire  cell  decreases  somewhat  in  size.  Here  again  be- 
comes manifest  the  difference  in  behavior  of  the  two  cell-coverings, 
the  plasmic  membrane  and  the  dead  membrane  (cell-wall).  The 
cell-wall  contracts  a  given  amount,  corresponding  to  its  previous 
expansion.  If  the  wall  is  very  delicate  and  the  action  of  the  solu- 
tion very  sudden,  it  may  be  thrown  into  folds  and  may  finally 
collapse.  As  a  rule  the  action  of  the  external  solution  is  sufficiently 
slow  and  the  cell-wall  of  sufficient  thickness  to  escape  such  deform- 
ity, in  which  case  the  primordial  utricle  is  removed  from  the  inner 
cell-wall,  corresponding  to  the  decrease  in  volume  of  its  interior. 
This  continues  and  the  space  between  cell-wall  and  utricle  is  filled 
by  the  solution  from  the  outside  and  the  inner  cell  solution.  This 
behavior  of  the  primordial  utricle  with  certain  concentrated  salt 
solutions  is  also  shown  with  certain  dilute  poisonous  liquids,  as  for 
example  iodine  solution,  and  dilute  acids.  A  longer  or  shorter  ex- 
posure will  kill  the  cell.  The  primordial  utricle  no  longer  permits 
all  substances  in  aqueous  solution  to  pass  alike.  In  the  case  of 
plasmolysis  this  fact  becomes  known  by  the  great  contraction  of 
the  primordial  utricle,  so  that  it  collects  as  a  lump  either  in  the 
centre  or  near  one  side  of  the  cell.  If,  conversely,  cells  filled  with 
cell-sap,  as  for  example  those  of  beet-root,  are  placed  in  pure 
water,  for  hours  no  sugar  will  pass  into  the  surrounding  liquid, 
although  the  membrane  in  itself  certainly  allows  sugar  to  pass. 
Upon  this  impermeability  of  the  living  utricle  to  certain  substances 
rests  the  possibility  of  producing  within  the  cell  a  high  hydrostatic 
pressure,  amounting  at  times  to  ten  or  more  atmospheres.7  (PFEF- 
FER'S  investigations.)  The  apparent  elective  choice  which  plants 
show  in  regard  to  the  appropriation  of  food-substances  does  not 


1  Owing  to  the  lack  of  a  corresponding  English  noun  I  have  retained  the 
original. — Trans. 

*  This  subject  will  again  be  referred  to  under  Water -movements  and  Tissue- 
tension. 


THE  CELL.  9 

depend  upon  this  plasmic  impermeability.  This  term  should  be 
used  with  caution.  There  certainly  is  no  subjective  choice. 
Whether  a  given  substance  is  taken  up  by  the  plant  depends  upon 
whether  it  is  of  use  or  not.  The  unequal  utilization  of  certain  sub- 
stances by  different  plants  depends  upon  inherent  peculiarities  of  the 
plants.  For  example,  of  two  plants  growing  in  the  same  soil  one 
will  take  up  much  and  the  other  little  silica  (SiO2),  the  one  much 
and  the  other  little  calcium  carbonate,  and  deposit  it  in  the  cell- 
walls.  The  above-mentioned  behavior  of  plasm  toward  poison- 
ous solutions  is  quite  different  and  might  in  a  certain  sense  justify 
the  term  choice.  It  is,  however,  strictly  speaking  only  the  reaction 
of  the  living  plasm  to  chemical  stimuli. 

For  the  investigations  concerning  plasmolysis  we  are  indebted 
to  several  authors,  NAGELI,  PRINGSHEIM,  PFEFFER,  and  more  recently 
HUGO  DE  YRIES.  To  the  last-mentioned  investigator  we  are  indebted 
for  a  very  important  treatise  entitled  the  <;  Analysis  of  the  Turgor 
Force." l  This  analysis  was  made  by  determining  the  so-called  "iso- 
tonic  coefficients."  I  will  select  only  the  following  statements 
from  the  work  of  de  Yries.  The  weakest  solution  (expressed  in 
gram. molecules,  not  per  cents)  of  potassium  nitrate  (JOsTO3)  which 
is  just  capable  of  inducing  plasmolysis  within  a  cell  has  the  same 
attractive  force  for  water  as  any  other  diosmotic  combination,  as  for 
example  oxalic  acid,  which  is  sufficiently  diluted  to  just  induce 
plasmolysis.  Such  concentrations  of  equal  tension  are  said  to  be 
4'isotonic."  Chemically  related  substances  have  the  same  coeffi- 
cient. If  the  isotonic  coefficient  of  KNO3  is  3,  then  it  is  also  3  for 
NaCl,  KC1,  in  fact  for  all  alkaline  salts  with  one  atom  of  the  metal 
in  a  molecule.  For  organic  compounds  such  as  malic  acid,  citric 
acid,  acetic  acid,  the  coefficient  is  2,  as  has  been  determined  by 
actual  experiment.  For  alkaline  salts  with  two  univalent  acid  radi- 
cles, as  for  example  MgCl3,  CaCl2,  it  is  4,  etc.  De  Yries  further 
determined  chemically  the  various  combinations  in  the  cell-sap  and 
then  found  the  turgor  force  exerted  by  each  (sum-total). 

The  relation  between  turgor  and  growth  will  be  referred  to  in 
the  chapter  on  "  Physiology  of  Growth." 

Before  entering  upon  the  discussion  of  the  cell-contents  it  should 
be  noted  that  the  contracting  primordial  utricle  carries  with  it  all 
the  solid  constituents  of  the  cell-contents  ;  also  that  the  priraor- 


Analyse  der  Turgorkraft,  Pringsheim's  Jahrbiicher,  XIV  (1884). 


10  COMPENDIUM  OF  GENERAL  BOTANY. 

dial  utricle  sometimes  ruptures  during  sudden  artificially  induced 
plasmolysis. 

III.  CELL-CONTENTS. 

Tedious  microscopic  examinations  of  the  cell-contents  aided  by 
staining  methods  have  recently  brought  to  light  a  series  of  facts 
and  form-relations.  But  so  far  no  conclusions  of  considerable 
importance  have  resulted  therefrom.  The  partially  compiled  and 
partially  original  communications  of  A.  ZIMMERMANN  '  are  especially 
suited  to  give  a  comprehensive  view  of  the  work  done  and  our 
present  knowledge  of  the  subject.  The  most  important  results  of 
the  above-mentioned  investigations  were  obtained  by  the  study  of 
the  nucleus  and  the  amyloplastids  (starch-builders).  STRASBURGEK, 
GUIGNAKD,  HEUSEK,  SCHMITZ,  KLEBS,  ZACHARIAS,  HABERLANDT,  and 
others  have  made  special  studies  of  the  nucleus,  while  SCHIMPER. 
has  devoted  much  attention  to  the  amyloplastids. 

For  the  sake  of  clearness  it  is  no  doubt  permissible  to  select 
from  a  subsequent  chapter  a  few  statements  concerning  cell-forma- 
tion before  taking  up  the  cell-inclusions. 

In  general  cells  originate  in  two  ways :  by  division  and  by  free 
cell-formation.  In  the  first  case  the  form  of  the  mother-cell  and 
the  position  of  the  septum  determines  the  form  of  the  daughter- 
cells.  In  the  second  case  the  daughter-cells  are  approximately 
spherical  and  float  freely  within  the  contents  of  the  mother-cell. 
In  both  cases  the  cells  grow  after  they  have  formed.  Deposits  may 
be  made  in  all  parts  of  the  cell-wall — uniform  surface  growth — or 
only  at  one  portion — apical  growth  of  cell.  In  the  latter  case  the 
cell  will  gradually  become  more  and  more  elongated. 

A.  LIVING  INCLUSIONS  OF  THE  CYTOPLASM. 

(a)  Nucleus. 

1.  The  nucleus  is  a  more  dense  plasmic  structure  and  is  usually 
present  in  all  cells,  though  it  is  difficult  to  prove  its  existence  in  the 
fungi.  Some  very  large  cells,  as  for  example  of  Caulerpa  (an  alga) 
which  are  often  a  foot  or  more  in  length,  contain  many  nuclei ;  long 
bast-cells  contain  several  nuclei.  The  majority  of  cells,  hence  those 

1  Die  Morphologic  und  Physiologic  der  Pflanzenzelle.  Breslau,  1887.  Beitrage 
zur  Morphologic  und  Physiologic  der  Pflanzeiizelle,  I,  II,  III.  Tubingen,  1890, 
1891,  1893. 


THE  CELL.  11 

of  microscopic  size,  contain  only  one  nucleus.  A  similarity  in  the 
form  of  the  nucleus  to  that  of  the  cell  is  not  noticeable.  In  the 
younger  cells  it  is  approximately  spherical ;  after  the  period  of  cell- 
growth  it  becomes  more  ellipsoidal.  It  often  lies  near  the  cell-wall 
imbedded  in  the  plasm,  sometimes  it  is  suspended  in  the  cell-lumen 
by  means  of  plasmic  threads.  To  demonstrate  the  presence  of  the 
nucleus  it  is  advisable  to  kill  the  cell  with  concentrated  picric  acid, 
which  "  fixes "  the  plasm,  and  subsequently  to  stain  it  red  with 
hsematoxylin  solution  or  green  with  methyl  green. 

The  nucleus,  again,  contains  one  or  more  nucleoli.1  The  nucleus 
(exclusiue  of  nucleoli)  contains  besides  true  albuminous  substances- 
a  characteristic  compound  or  group  of  compounds  also  albuminoid 
in  nature,  namely,  the  phosphorus-bearing  nuclein.  It  swells  in  a 
10%  solution  of  NaCl  and  is  dissolved  in  a  solution  of  potassium 
hydrate  which  distinguishes  it  from  true  albumen. 

As  a  rule  the  nucleus  is  located  in  that  portion  of  the  cell  where- 
growth  (growth  in  thickness  or  surface  of  cell-wall)  is  the  most 
active  or  where  it  continues  the  longest.  Usually  the  nucleus  assumes- 
a  definite  position  only  in  the  undeveloped  cell,  later  the  position  is 
indefinite.  Rarely  it  may  assume  a  definite  position  for  a  second 
time. 

From  the  foregoing  statements  it  is  to  be  supposed  that  the- 
nucleus  is  of  special  significance  in  the  processes  of  cell-growth. 
What  role  it  really  does  play  and  what  functions  it  subsequently 
subserves  is  still  a  question.  The  observations  made  by  KLEBS  upon 
artificially-divided  cells  are  of  special  interest.  It  was  observed  that 
only  that  portion  of  the  cytoplasm  which  contained  the  nucleus  is- 
capable  of  growing  in  length  and  surrounding  itself  with  a  mem- 
brane, while  the  function  of  the  remainder  is  assimilation  only. 

The  difference  between  cell-division  and  free  cell-formation  isr 
according  to  our  present  knowledge  of  nuclear  behavior,  not  so 
great  as  was  formerly  taught.  During  each  cell-division  and  in 
general  during  each  free  cell-formation  there  is  a  nuclear  division. 
The  so-called  indirect  nuclear  division  occurs  most  frequently,  and 
is  connected  with  extensive  changes  in  the  nuclear  substance.  The 
details  of  this  mode  of  nuclear  division  have  been  made  known  by 
STRASBTJRGER,  FLEMMING,  GUIGNARD,  and  HEUSER. 

I  will  not  enter  into  a  comprehensive  description  of  indirect 


There  are  often  denser  portions  noticeable  within  the  nucleoli.— Trans. 


12  COMPENDIUM  OF  GENERAL  BOTANY. 

nuclear  division  or  "  karyokinesis,"  but  will  limit  myself  to  the 
explanation  of  the  Lccompanying  figures.  One  usually  distinguishes 
a  "  chromatin  "  and  an  "achromatin"  nuclear  figure.  The  former 
is  distinguished  by  the  readiness  with  which  the  nuclein  is  colored  by 
various  stains,  the  latter  is  composed  of  the  slightly  staining  portions 
of  the  nuclear  substance.  In  the  illustrations  the  chromatic  figure  is 


FIG.  3. — Successive  stages  of  nuclear  division.1     (After  Strasburger.) 

In  A  an  irregularly  wound  thread  is  formed  from  the  nuclear  network  (spirem,  Knauel).  In 
B  and  Care  seen  the  "  chromatin-granules  "  resulting  from  the  breaking  up  of  the  chromatin. 
At  .Band  Fa,  certain  arrangement  and  longitudinal  division  of  chromatin-threads  takes  place. 
Somewhat  previous  to  this  the  achromatin  nuclear  figure  makes  its  appearance  (delicate  lines 
in  E&nd  F).  The  two  halves  of  the  chromatin-threads  move  along  the  fine  achromatin  lines  in 
opposite  directions  to  the  poles  (J)and  form  the  "  spirem"  (Knauel)  stage  of  the  daughter-cells 
<M,  O).  Out  of  the  spirem  is  formed  the  network,  nucleoli  appear,  also  a  nuclear  membrane, 
and  the  daughter-nuclei  are  complete.  When  a  septum  is  to  be  formed  a  cellulose  plate  forms 
between  the  two  daughter-nuclei  at  the  points  where  the  thickenings  occur  on  the  nuclear 
spindle;  otherwise  the  nuclear  spindle  (achromatin-figure)  disappears  with  the  thickenings. 

indicated  by  heavy  dark  lines,  the  achromatin  figure  by  light  lines 
•(E,  F,  J,  M).  Roux  assumes  hypothetically  that  the  purpose  of 
karyokinesis  is  to  transmit  hereditary  peculiarities  by  means  of  the 
dividing  decisive  substances  (chromatin  threads  or  bands).  How- 


1  In  connection  with  indirect  nuclear  division  should  also  be  mentioned  the 
recently  discovered  and  studied  "  centrospheres "  or  "directive  spheres,"  small 
spherical  bodies,  normally  two  in  number,  lying  just  outside  of  the  nucleus,  which 
also  undergo  considerable  change  in  position  during  nuclear  division. — Trans. 


THE  CELL. 


ever,  the  same  uncertainty  still  surrounds  "  heredity  "  as  it  does  the 
"idioplasm  "  of  Nageli. 

A  process  directly  opposite  to  that  of  nuclear  division  is  the 
union  of  nuclei.  This  process  evidently  plays  a  part,  though  un- 
explained, in  reproduction,  in  the  fertilization  of  one  cell  by  another. 
(See  chapter  on  Reproduction.) 

(b)  Chlorophyll  Grains,  Chromoplastids,  Leucoplastids. 

These  three  structures  are,  as  has  been  indicated,  included  under  the 
name  chromatophores.  A  discussion  of  chlorophyll  bodies  will  lead 
to  the  discussion  of  chromoplastids  and  leucoplastids. 

In  all  chlorophyll  bodies  there  is  a  green  coloring  matter, 
chlorophyll.  It  is  intimately  associated  with  the  highly  important 
function  of  carbon  assimilation,  which  will  be  discussed  later.  Even 
in  the  carbon-assimilating  plants  of  a  red-brown  or  blue-green 
color  (as  for  example  red  and  brown  marine  algae)  it  is  assumed 


FIG.  3.     (After  Sachs.)  FIG.  4. — A  portion  of  prismatic  cell 

with    lateral    chlorophyll  -  bodies 
(schematic). 

Optical  cross-section  at  q;  surface  view 
at/;  optical  longitudinal  section  at  I. 

that  they  contain  active  chlorophyll,  but  that  it  is  hidden  by  some 
other  coloring  matter.  Among  vascular  plants  there  are  also  nu- 
merous instances  where  the  chlorophyll-bearing  cells  are  colored  red 
by  the  cell-sap.  Among  phanerogams,  vascular  cryptogams,  and 
mosses  the  chlorophyll  bodies  are  disk-shaped,  though  usually 
spoken  of  as  "  chlorophyll  grains."  These  disks  lie  with  the  flat 


14  COMPENDIUM  OF  GENERAL  BOTANY. 

surface  in  contact  with  the  thin  primordial  utricle,  thus  having  the 
appearance  of  being  in  contact  with  the  cell-wall.  Among  the 
algae  the  chlorophyll  bodies  may  assume  the  form  of  disks,  bands, 
plates,  or  even  radiate  like  a  star.  In  the  Palmellacece  (unicellular 
algae)  the  plasmic  body,  with  the  exception  of  the  nucleus  and  hyalo- 
plasm, is  colored  green.  Among  the  PhycochromacecB  (nucleus 
wanting)  there  are  no  differentiated  chlorophyll  bodies,  but  the  entire 
plasmic  body  is  homogeneously  colored.  Spiral  chlorophyll  bands 
are  seen  in  Spirogyra  (Fig.  3),  which  also  has  a  nucleus  suspended 
in  plasmic  threads.  A  portion  of  a  palisade  cell  (typical  assimilating 
•cell  of  leaf)  with  chlorophyll  bodies  is  shown  in  Fig.  4. 

Origin  of  Chlorophyll  Bodies. — Chlorophyll  bodies  often  result 
from  direct  division.  When  a  chlorophyll-bearing  algal  cell  di- 
vides, each  daughter-cell  receives  a  part  of  the  chlorophyll,  which 
part  continues  to  increase  by  growth  or  division.  Young  cells  in 
growing  areas  (apical  areas),  as  for  example  in  the  stems  of  the  higher 
plants,  are  supplied  with  a  colorless  plasm.  It  is,  however,  supposed 
that  these  cells  contain  leucoplastids,  that  is  colorless  plasmic 
bodies  which  may  become  green  on  exposure  to  sunlight.  No  doubt 
the  unicellular  embryo  contains  besides  nuclear  substance  also  leuco- 
plast  substance,  and  that  there  is  no  development  de  novo  of  either. 
Both  multiply  by  division.  (SCHMITZ,  SCHIMPER,  MEYEK.)  Under 
•certain  conditions  leucoplastids  may  be  converted  into  chrornoplas- 
tids,  that  is  non-chlorophyllous  coloring  bodies.  The  first  of  the 
two  important  functions  (chlorophyll  and  starch-forming)  of  leuco- 
plastids has  thus  only  been  touched  upon.  The  leucoplastids  are 
also  found  in  tissues  devoid  of  chlorophyll  where  starch  is  formed 
from  pre-existing  dissolved  products  of  assimilation,  as  for  example 
in  the  potato-tuber.  These  leucoplastids  are  called  "  starch-builders  " 
(SCHIMPEK)  because  they  develop  starch-grains;  either  on  their 
periphery  or  within  the  interior,  similar  to  chloroplastids  with  the  aid 
of  sunlight ;  but  with  the  important  difference  that  in 
the  latter  case  the  raw  materials  are  CO,  and  H2O, 
while  in  the  case  of  the  starch-builders  the  starch- 
grain  is  formed  from  dissolved  starch,  or  more  gener- 
ally from  assimilated  food-substances  brought  from 
the  green  cells.  The  nature  of  the  starch-builder  can 
be  explained  best  in  connection  with  a  chlorophyll-grain  (Fig.  5, 
cell  Z).  The  chlorophyll-bodies  are  represented  as  producing  starch- 
bodies  on  the  periphery  at  c'  and  within  the  interior  at  c".  The 


THE  CELL.  15 

starch-builder  (amyloplastid)  is  colorless  and  forms  starch  within  or 
upon  it  in  the  manner  described. 

Leucoplastids  are  very  unstable  and  easily  destroyed,  hence  not 
readily  demonstrable.  In  the  living  cell  they  must  be  rapidly 
acted  upon  by  certain  reagents,  as  for  example  an  aqueous  iodine 
solution.  Their  form  is  usually  spherical,  sometimes  elongated  or 
spindle  shaped  owing  to  the  presence  of  crystalloids. 

The  chromoplastids  form  the  coloring  substances  of  the  variously 
colored  flower  and  fruit  parts.  One  fact  is  to  be  remembered, 
namely,  that  the  red,  blue,  and  violet  colors  are  often  due  to  sub- 
stances in  solution  in  the  cell-sap.  Yellow  chromoplastids,  for 
example,  are  found  in  the  cells  of  the  beet.  The  form  of  the 
chromoplastids  varies ;  they  may  be  spheroidal,  disk-like,  radiate,  or 
elongated. 

At  this  point  it  is  well  to  make  a  few  statements  concerning  (1) 
metamorphosis;  (2)  the  destruction  of  chlorophyll  (SACHS,  G.  KRAUS). 

1.  Chlorophyll  bodies  may  be  converted  into  red  chromoplastids, 
thus  causing  the  red   coloring  of  fruits.     This  has    been  demon- 
strated in  many  instances.     The  red  detected  in  the  winter  color- 
ation of  evergreen  leaves  (Conifers,  Buxus)  disappears  in  the  spring. 
In  these  plants  the  chlorophyll  bodies  are  not  entirely  destroyed  ; 
they  lose  only  a  portion  of  the  green  coloring  matter,  while  carmine- 
red  drops  appear  which  again  disappear  in  the  early  spring. 

2.  On  the  other  hand  the  autumn  coloration  of  falling  leaves, 
the  yellowness  of  straw,  the  change  in  color  of  dying  plants  or  parts 
of  plants,  is  due  to  the  destruction  of  the  chlorophyll..    The  entire 
plasm  and  the  chlorophyll  bodies  of  falling  leaves  enter  into  dis- 
solution and  the  important  constituents  pass  into  the  more  persist- 
ent parts.     A  yellow  coloring  matter  (xanthophyll)  remains  in  the 
leaves  in  the  form  of  small  granules.     In  the  case  of  the  red  coloring 
of  falling  leaves  there  is  in  addition  to  these  yellow  granules  a  red 
cell-sap  (grape). 

There  is  still  another  plasmic  structure  to  be  mentioned  which 
the  more  delicate  microscopic  manipulations  have%  brought  to  our 
notice,  namely,  the  so-called  "  starch  or  amylum  clusters "  or 
"  pyrenoids."  In  composition  they  resemble  most  nearly  the 
nucleoli  or  nucleus.  They  are  found  almost  exclusively  among  the 
algae,  where  they  usually  occur  within  the  chlorophyll  bodies,  evi- 
dently constituting  centers  of  starch-formation.  As  a  rule  they  are 
enveloped  by  numerous  starch-granules,  hence  the  name. 


16          COMPENDIUM  OF  GENERAL  BOTANY. 

Those  organized  plasmic  masses  which  represent  the  fertilizing 
elements  in  reproduction  will  be  referred  to  in  the  chapter  on  Re- 
production. Before  passing  to  the  consideration  of  the  dead  inclu- 
sions of  cytoplasm  we  will  mention  a  few  special  plasmic  structures 
whose  significance  is,  in  part,  not  well  understood. 

1.  Cilia  (Wimpern,  flagella)  of  swarm-spores  and  spermatozoa 
serve   as   organs   of   movement.      Their   number  and   manner   of 
attachment  vary  greatly  (one  or  two,  covering  the  body  entirely,  or 
only  partly).     The  cilia  of  spermatozoa  originate  in  the  cytoplasm  ; 
they  are  not  nuclein. 

2.  The  so-called  eye-spot  (red  or  red-brown)  in  swarm-spores  of 
algae  had  already  been  noticed  by  earlier  authors.     Morphologically 
it  belongs  to  the  chromatophores  (KLEBS).     It  k  said  to  be  very 
sensitive  to  mechanical  pressure  and  to  certain  alkaloids.     Its  func- 
tion is  unknown. 

3.  The  iridescent  plasmic  plates  in  the  superficial  cells  of  various 
marine  algae   probably  serve  to  protect  the  chromatophores  from 
intense  light  (discovered  by  BEBTHOLD). 

4.  In  root-tubercles  of  Leguminosae  there  are  constantly  found 
certain    proteid    bodies    resembling     bacteria,    called    bacteroids1 
(Brunchorst).     They  eventually  serve  the  purpose  of  converting 
nitrogen-bearing  organic  compounds  into  albuminoid  substances. 

We  will  now  turn  our  attention  to  the  dead  inclusions  of 
cytoplasm. 

B.  DEAD  INCLUSIONS  OF  CYTOPLASM. 

Dead  inclusions  as  distinct  from  "plasmatic"  inclusions  play 
only  a  passive  role  in  plant  chemistry.  This,  however,  does  not 
make  their  physiological  significance  any  less  important.  In  the 
discussion  of  many  of  these  structures  I  shall  adhere  in  general  to 
A.  ZTMMERMANN'S  a  treatment  of  them  :  this  also  will  hold  true  of 
my  treatment  of  the  general  morphology  of  the  cell. 

In  mass  and  importance  starch-grains  stand  first.  Almost 
equal  to  them  in  importance  but  of  less  frequent  occurrence  are  the 
aleuron-grains  (gluten),  including  the  protein-crystalloids.  To  these 
must  be  added  fat-crystals,  solid  coloring  substances,  and  mineral 
excretions,  especially  in  the  form  of  crystals. 


1  These  bacteroids  are  now  generally  admitted  to  be  true  bacteria  belonging  to 
the  Schizomycetes.   Their  development  has  been  observed  in  culture  media. — Trans. 
'Die  Morph.  und  Phys.  der  Pflanzenzelle.     Breslau,  1887. 


THE  CELL. 


17 


The  two  first  named  substances  (starch-grains  and  aleuron-grains) 
are  represented  highly  magnified  in  the  figures  shown  below.  Fig.  6 
represents  both  starch  and  aleuron  as  they  occur  in  seeds  of  Pisum 
sativum  (pea).  Fig.  7  represents  starch-grains  from  a  potato-tuber. 

(a)  Starch. 

In  1858  NAGELI  made  known  the  results  of  his  investigations 
relative  to  the  growth  of  substances  capable  of  imbibition  (as  opposed 
to  crystals),  especially  starch-grains  and  cell-membranes.  The  chief 
conclusion  arrived  at  is  that  growth  of  starch-grains  and  cell-walls  is 
~by  intussusception  and  not  by  apposition  as  in  crystals.  (The  cell- 
wall  will  be  discussed  later.) 

Stratification  of  starch-grains  is  not  the  result  of  deposits  of 
successive  layers  so  that  the  outermost  layer  is  the  youngest.  On 


FIG.  6.—  Cells  from  the  seed  of  Pisum 

sativum. 
(X  800.)    (After  Sachs.) 


FIG.  7. 

A,  simple  starch-grain  of  potato-tuber; 
5,  partial  compound  ;  C,  compound.  (X  800.) 


the  contrary  the  layers  are  the  result  of  internal  processes  of  growth 
arid  differentiation  :  there  is  nothing  superimposed  upon  the  outer- 
most layer,  which  really  existed  from  the  very  beginning.  The 
cause  of  the  stratification  is  to  be  found  in  the  alternating  layers  of 
greater  and  lesser  percentage  of  water  (therefore  more  and  less  dense 
layers);  since  excessive  evaporation  or  absorption  of  water  causes 
them  to  become  less  distinct.  Optically,  by  the  aid  of  the  polariza- 
tion microscope,  it  can  be  shown  that  starch-grains  react  as  though 
composed  of  uniaxial  crystals.  Under  the  crossed  Nicol  prisms 


18  COMPENDIUM  OF  GENERAL  BOTANY. 

there  appears  a  bright  rectangular  cross  whose  arms  form  an  angle 
of  45°  with  the  polarization  plane  of  the  nicols, 

Of  Nageli's  arguments  in  favor  of  growth  by  intussusception  I 
will  now  mention  the  particular  one  which,  according  to  SCHIMPER'S  * 
more  recent  investigations,  can  no  longer  be  maintained.  Fig.  7 
shows  two  u  compound  "  starch-grains.  According  to  Nageli  these  are 
usually  the  result  of  differentiations  within  the  starch-grain  (usually 
nuclear  division)  and  only  exceptionally  through  the  fusion  of 
two  individual  grains.  Schimper  has  demonstrated  for  a  large 
number  of  plants  that  subsequent  fusion  of  individual  starch- 
grains  does  take  place. 

The  theory  of  intussusception,  whose  acceptance  is  favored  by 
reasons  to  be  given  below,  teaches  that  starch-substance  in  solution 
(for  example  glucose),  hence  starch-molecules  and  water-molecules, 
passes  into  the  interior  of  the  growing  starch-grain,  and  that  from 
this  material  new  molecular  layers  are  formed  and  the  size  and 
density  of  already  existing  molecular  masses  are  increased.2  The  in- 
crease in  density  of  the  starch-substance  depends  upon  the  increase 
in  size  of  the  molecules  which  grow  by  apposition,  similar  to  crystals. 

The  following  evidence  and  considerations  speak  in  favor  of  the 
intussusception  theory  :  1.  In  the  earliest  stage  the  starch-grain  con- 
sists of  a  uniformly  dense  substance :  such  is  the  nature  of  the  very 
small  grains;  however,  as  soon  as  they  increase  in  size,  there  is  formed 
a  softer,  more  watery  (not  denser)  nucleus  or  central  layer.  2.  The 
outermost  layer  of  the  growing  starch-grain  is  always  more  dense. 
3.  The  demonstrated  presence  of  the  internal  tensions  of  the  starch- 
grain  also  harmonizes  with  Nageli's  theory.  In  the  outer  layer  of 
the  young,  still  firm,  spherical  starch-grain  there  originates  and 
exists  a  positive  tension  ;  in  the  interior  a  negative  tension.  The 
outer  layer  receives  the  first  and  greatest  food-supply,  and  as  a 
result  it  is  first  to  increase  in  area.  When  the  negative  pressure  in 
the  interior  mass  (plus  the  effort  to  deposit  food-material)  has  reached 
a  certain  height,  the  soft  nucleus  (hilum)  is  formed.  Similar 
processes  take  place  in  the  outer  dense  layer ;  this  is  repeated 
again  and  again.  It  may  be  stated  here  that  Nageli  believes  the 
causes  for  these  molecular  changes,  namely,  the  attraction  of  starch- 
particles  for  each  other  and  for  water,  to  be  certain  molecular 


1  Botanische  Zeitung,  1880,  1881. 
•NAGBLI,  Starkekoruer,  S.  291. 


THE  CELL.  19 

forces  "  whose  nature  is  unknown" l  Kageli  has  probably  ad- 
vanced as  far  as  it  is  possible  to  go  in  this  field  of  investigation.  He 
has  reached  the  given  forces  inherent  in  the  smallest  particles  of 
matter. 

The  above  does  not  compel  us  to  accept  the  intussusception 
theory.  However,  it  cannot  be  denied  that  the  evidence  given 
explains  certain  phenomena  more  satisfactorily  than  the  apposition 
theory. 

It  would  be  very  desirable  to  establish  a  definite  reliable  life- 
history  of  a  starch-grain  ;  to  observe  directly  its  development  from 
beginning  to  end,  for  example  in  a  culture  medium.  We  arrive  at 
the  conclusion  of  " younger"  and  "older"  stages  of  starch  develop- 
ment in  an  abstract  way  by  describing  as  many  stages  or  condi- 
tions as  we  happen  to  observe.  Conclusions  as  to  age  are  then  in- 
directly reached  according  to  the  size  of  the  starch-grain  under 
examination  and  by  other  considerations. 

The  opinion  of  ARTHUR  MEYER  8  that  stratification  of  starch- 
grains  is  the  result  of  fermentation  (dissolving  effect)  combined  with 
periodic  apposition  is  opposed  by  KRABBE,  3  according  to  whose 
investigations  diastase,  the  starch-dissolving  ferment,  always  acts  on 
the  exterior  and  never  enters  the  starch-substance  no  matter  how 
deep  or  variable  the  corrosions  may  appear.  It  must  be  observed 
that  this  corrosion  as  the  result  of  solution  by  means  of  diastase 
is  still  an  unexplained  phenomenon. 

The  following  statements  will  assist  in  explaining  the  minute 
structure  of  starch-grains.  When  a  fresh  starch-grain  becomes  dry 
crevices  are  formed  in  a  radial  direction  at  right  angles  to  the  strati- 
fications. In  the  interior  where  the  split  begins  there  is  a  hollow 
space ;  the  crevices  become  narrower  outward.  The  fact  that  the 
greatest  loss  of  water  is  in  the  interior  and  in  the  radial  directions 
of  the  crevices  indicates  (1)  that  the  entire  starch-grain  contains 
gradually  more  water  from  without  inward,  and  (2)  that  in  every 
layer  or  stratum  the  deposition  of  water-molecules  is  more  active 
in  the  tangential  direction  than  in  the  radial,  since  cohesion  is  less 
in  the  tangential  direction. 

Chemical  Properties  and  Solution  of  Starch-grains. — To  test 
the  presence  of  starch  microscopically  we  resort  to  one  of  the  few 


1  Starkekorner,  p.  332. 

2  Botaiiische  Zeitung,  1881. 
3Prmgsbeirn's  Jabrbiicber,  1890. 


20  COMPENDIUM  OF  GENERAL  BOTANY. 

valuable  microchemical  tests,  namely,  blue  coloration  with  an 
aqueous  iodine  solution.  Previous  boiling  of  the  starch-bearing 
substance  in  water  is  recommended.  "When  the  quantity  of  starch 
is  very  small,  Arthur  Meyer's  plan  will  be  found  useful.  It 
consists  in  decolorizing  and  extracting  the  plant-substance  by  means 
of  alcohol  and  then  adding  iodine  in  a  chloral-hydrate  solution. 

Only  the  percentage  composition  is  known  which  corresponds 
to  that  of  cellulose  :  ?i(C6H10OB).  According  to  NAGELI  jun.  and 
ARTHUR  MEYER  starch-grains  do  not  consist  of  two  or  more  starch 
modifications  as  was  formerly  believed  by  NAGELI  sen.  Red  or 
reddish-brown  coloration  with  iodine  simply  demonstrates  an 
association  with  arnylodextrin. 

The  ferment  diastase,  which  plays  such  an  important  part  in 
germinating  cereals  by  virtue  of  its  starch-dissolving  effect,  has 
already  been  mentioned.  Its  true  nature  and  method  of  action  is 
still  unknown.  Other  substances,  such  as  dilute  acids,  through  long- 
continued  action  will  also  dissolve  the  entire  mass  of  starch-grains- 
(Nageli  jun.). 

The  behavior  of  starch-grains  with  water  is  especially  interesting. 
Due  to  internal  (molecular)  causes,  dry  but  otherwise  intact  starch- 
grains  "  imbibe  "  a  definite  amount  of  water.  There  is  besides  this- 
imbibition  a  swelling  due  to  external  causes.  This  swelling  is 
caused  by  a  greater  or  lesser  absorption  of  water  at  a  high  tempera- 
ture, or  by  the  addition  of  acids  or  alkalies.  If  such  a  swollen 
starch-grain  is  dried  and  again  supplied  with  water  it  no  longer 
assumes  its  former  volume ;  its  structure  has  become  modified, 
something  which  never  follows  "imbibition"  (Nageli,  Correns). 
Our  foods  (as  boiled  potatoes,  peas,  bread)  contain  paste  (that  is,, 
swollen  starch),  since  they  have  been  exposed  to  high  temperatures. 
This  swollen  starch  is  subsequently  converted  into  soluble  sugar  by 
means  of  the  saliva  (ptyalin)  and  the  pancreatic  juice  (amylopsin). 

We  shall  now  add  a  few  remarks  on  the  morphology  of  starch- 
grains,  especially  as  to  their  form  and  size.  In  many  instances  not 
only  genera  and  species  but  entire  families  may  be  recognized  by 
characteristic  starch-grains.  Potato-starch  is  characterized  by  an  ex- 
centric  nucleus  (hilum),  and  is  of  oval  or  conical  form.  Starch- 
grains  of  the  LeguminoscB  (seeds)  are  oval  with  a  concentric  hilum  ; 
those  of  our  indigenous  cereals  are  lentil-shaped,  very  small  and  with 
concentric  hilum  ;  those  from  the  milky  juice  of  Euphorbia  species- 
are  dumbbell-shaped.  The  smallest  starch-grains  approach  the- 


THE  CELL.  21 


limits  of  vision  (1  micromillimeter  =  y^Vo  mm*  =  I/**  or  I688)- 
The  longest  simple  grains  are  often  185yu  in  length.  The  largest 
-compound  starch-grains  measure  as  much  as  106/*  in  length.  , 

Both  starch  and  aleuron  in  the  cells  of  Pisum  sativum  (Fig.  6), 
are  also  of  importance  to  the  physiology  of  nutrition  in  man. 
The  seeds  of  Leguminosce  contain  two  of  the  most  important 
representatives  of  our  food-materials  :  starch,  a  carbohydrate,  and 
aleuron,  an  albuminoid  ;  hence  both  non-nitrogenous  and  nitrogenous 
food-substances. 

(b)  Aleuron-grains. 

Aleuron-grains  or  protein-grains  ("  Klebermehl  "  of  THEO. 
HARTTG)  form  the  principal  albuminoid  reserve  materials  in  the 
seeds  of  phanerogams,  while  starch-grains  form  the  chief  carbo- 
hydrate reserve  products.  In  order  to  observe  the  aleuron  grains  it 
is  advisable  to  fix  them  with  a  2$  alcoholic  sublimate  solution.1  As 
a  rule  they  are  much  smaller  than  the  accompanying  starch-grains  ; 
they  may,  however,  reach  a  considerable  size.  The  aleuron-grains 
consist  of  a  basal  substance  and  chemically  different  inclusions. 
The  base  is  albuminoid  ;  the  inclusions  are  either  crystalloids,  amor- 
phous spherical  bodies  ("  globoids  "),  or  calcium  oxalate  crystals. 
Of  these  three  inclusions  sometimes  more  than  one  is  represented  in 
the  same  grain. 

(a)  The  crystalloids  resemble  the  base  in  that  they  are  albumin- 
oid, but  differ  in  being  insoluble  in  water  while  the  base  is  usually 
soluble.  They  differ  from  true  crystals  in  that  they  store  coloring  ma- 
terial and  are  capable  of  imbibition  and  swelling.  However,  accord- 
ing to  SCHIMPER  and  DUFOUR  their  similarity  to  crystals  is  perhaps 
greater  than  NAGELI  supposed.  Schimper  noticed  that  the  regular 
crystalloids  of  Ricinus  swelled  equally  in  all  directions  when  placed 
in  dilute  hydrochloric  acid  ;  while  in  the  hexagonal  crystalloids  of 
Musa  Hillii  the  swelling  was  equal  at  right  angles  to  the  main  axis. 
In  crystalloids  of  the  Para  nut  the  swelling  parallel  to  the  main  axis 
was  either  greater  or  less  than  at  right  angles  to  that  axis  ;  hence 
their  behavior  is  similar  to  that  of  hexagonal  crystals  in  response  to 
heat-expansion.  The  optical  behavior  is  also  analogous  to  that  of 
crystals  :  the  regular  crystalloids  are  isotropic,  the  hexagonal  slightly 
doubly  refractive.  A  special  peculiarity  of  some  crystalloids  is  a 
stratification  noticeable  in  the  swollen  state.  Fig.  8  A,  represents  a 

1  PFEFFER  studied  the  aleuron-grains  more  particularly. 


22  COMPENDIUM  OF  GENERAL  BOTANY. 

cell  suspended  in  oil ;  the  crystalloids  are  not  visible  because  they 
have  the  same  refractive  index  as  the  oil. 

(ft)  Globoids  may  be  studied  by  first  dissolving  the  aleuron  and 
eventually  also  the  crystalloids  by  means  of  dilute  potassium-hydrate 
solution.  The  globoids  are  not  soluble.  According  to  Pfeffer  they 
consist  of  a  double  phosphate  of  lime  and  magnesia.  The  smallest 
approach  the  limits  of  vision  ;  the  largest  are  about  10/*  in  dia- 
meter. They  are  amorphous  and  isotropic,  and  hence  produce  no 
polarizing  light  effects. 

(y)  Crystals  of  calcium  oxalate  are  usually  found  in  such 
aleuron-grains  as  contain  no  other  inclusions.  They  are  insoluble  in 


A  fi 

FIG.  8.  —Endosperm-cells  of  Ricinus  communis. 

A.  as  seen  suspended  in  oil;  B,  in  potassium  iodide-iodine  solution,    g,  globoid;  fc,  crystal- 
loid.   (After  Frank.) 

dilute  acetic  acid.  They  usually  occur  in  star-shaped  clusters 
(Krystalldrusen). 

The  several  inclusions  are  already  formed  before  the  develop- 
ment of  all  the  aleuron-grains,  and  are  subsequently  surrounded  by 
a  deposit  of  aleuron. 

Protein  crystalloids  (a)  not  only  occur  in  aleuron-grains,  but 
they  are  sometimes  also  found  in  the  nucleus,  frequently  within 
chromatophores  (associated  with  an  oily  substance),  and  sometimes 
in  the  cytoplasm  or  the  cell-sap. 

(c)  The  Remaining  solid  dead  Inclusions  of  the  Cell. 

Fat-crystals  seldom  occur,  although  fats  are  plentifully  distrib- 
uted in  the  cell.  This  is  because  the  plant-fats  are  liquefied  at 
ordinary  temperatures  and  are  therefore  classed  with  the  fatty  oils 
(page  24).  Solid  coloring  substances  are  found  here  and  there 


THE  CELL. 


23 


(blue  and  violet).  Some  of  the  Schizomycetes  (Beggiatoa)  secrete 
sulphur  within  the  cells.  Some  algae  (Desmidiacece)  secrete 
gypsum  (OaS04+2H,0). 

Calcium  oxalate  crystals  are  plentifully  distributed  in  the  cells 
of  the  entire  vegetable  kingdom.  In  most  instances  this  lime-salt 
remains  unchanged  wherever  formed.  Yery  generally  these  crystals 
appear  in  the  form  of  clusters  (Drusen) ;  frequently  they  occur  as 
acicular  bundles  called  raphides,  less  frequently  as  perfect  crystals. 
STAHL  studied  these  crystals,  especially  the  raphides,  in  regard 
to  their  function,  and  decided  that  they  served  as  a  protection  to 
the  plants  against  destruction  by  snails  and  grasshoppers.  (Feeding 
experiments.)  Fig.  9  shows  raphides;  Fig.  10,  perfect,  well-de- 
veloped crystals. 


FIG.  9. —Cells  from  the  stem  of  Trades-    FIG.  10. —Crystal-bearing  cells  of  Aesculus 
cantiazebrina.    (After  Haberlandt.)  Hippocastcmum.      (After  Haberlandt.) 

The  first  more  exact  studies  of  these  crystals  were  made  by 
HoLZNER.1  The  perfect  crystals  belong  either  to  the  tetragonal  or 
the  clinorhombic  system,  as  do  also  the  artificially  produced  crystals, 
this  depending  upon  whether  they  contain  one  or  three  molecules 
of  water  of  crystallization.  The  clusters  are  aggregates  of  usually 
not  very  small  crystal  individuals  around  a  nucleus  of  protein 


1  Flora,  1864. 


24  COMPENDIUM  OF  GENERAL  BOTANY. 

(albuminoid  substance).  Generally  these  crystals  originate  within 
the  cytoplasm.  As  proof  of  such  origin  we  have  in  addition  to  the 
albuminoid  nucleus  of  the  clusters  the  presence  of  an  albuminoid 
covering  to  such  crystals.  Sometimes  a  wall  of  cellulose  is  formed 
around  them.  It  must,  however,  be  noted  that  sometimes  no 
plasmic  covering  can  be  demonstrated. 

Silicious  bodies  ("Kieselkorper")  have  also  been  observed  within 
the  cell. 

As  will  be  seen  later,  these  same  substances  which  have  been 
mentioned  as  occurring  in  the  cell  may  also  impregnate  the  cell- 
wall.  We  shall  here  add  a  few  remarks  on  plant-mucilage,  though 
it  does  not  belong  to  the  solid  plasmic  inclusions.  Raphide — (see 
cells  foregoing)  usually  contain  a  mucilaginous  substance.  It  forms 
the  officinal  Salep  mucilage  of  Orchid  tubers.  It  seems  probable 
(FRANK)  that  this  substance  originates  within  the  plasm  as  a  spherical 
body  finally  enclosing  the  raphides  and  filling  the  entire  cell-lumen. 
STAHL,  whose  investigations  concerning  "  plants  and  snails  "  we  have 
already  mentioned,  ascribes  to  this  mucilage  enveloping  the  raphides 
the  function  of  an  "  expulsor"  of  the  acicular  crystals.  As  soon  as 
some  animal  wounds  the  cell,  the  mucilage  which  is  under  pressure 
partially  forces  out  the  sharp  needlelike  crystals.  The  raphides 
are  more  numerous  toward  the  outer  surface  of  the  tubers ;  the 
mucilage  is  more  abundant  toward  the  interior.  This  mucilage  also 
serves  as  reserve  material,  since  it  is  dissolved  when  the  tubers  begin 
to  sprout. — Plant-cells  may  also  contain  sph aero-crystals  of  calcium 
oxalate  besides  the  above-mentioned  perfect  forms. 

C.  THE  CELL- SAP  AND  THE  REMAINING  FLUID  CONTENTS  OF  THE 

CELL. 

The  fluid  filling  the  vacuoles,  or  more  often  in  mature  cells 
almost  the  entire  cell-lumen,  is  called  cell-sap.  It  contains  various 
substances  in  solution  :  glucose,  cane-sugar,  inulin,  asparagin,  organic 
acids,  inorganic  salts,  coloring  materials,  and  occasionally  still  other 
substances.  When  plant-tissue  is  placed  in  alcohol,  inulin  is 
deposited  in  the  form  of  sph  aero-crystals  (PRANTL).  Very  often  cell- 
sap  contains  red  and  blue  coloring  material  in  solution.  (Notwith- 
standing this  colored  cell-sap,  plasm  is  almost  without  exception 
colorless,  leaving  out  of  consideration  the  cliromatophores.) 

Oil-droplets  (chemically  not  easy  to  define)  and  equally  refractive 


THE  CELL.  25 

tannin-spheres,  are  of  frequent  occurrence  within  the  cell.  Fatty  oil 
often  supplants  starch  during  the  processes  of  nutrition.  Osmic 
acid  reacting  upon  these  oil-droplets  is  reduced  to  black  osmium. 
Alkanua  tincture  stains  the  oil-globules  red.  Tannin-spheres  and 
probably  other  chemically  related  substances  are  stained  brown  with 
potassium  bichromate.  According  to  STAHL  tannic  acid  serves  prima- 
rily as  a  "chemical  protector"  against  destructive  animals.  (For 
example,  snails  devoured  leached  clover-leaves  much  more  greedily 
than  fresh  ones.)  As  the  author  states,  this  fact  must  not  be 
considered  as  all-inclusive,  as  tannin  is  very  common  in  widely 
different  plant-tissues.  PFEFFEK*  expresses  the  opinion  that 
tannin  is  the  result  of  the  decomposition  of  albuminoid  substances. 
G.  KRAUS  a  (Halle),  to  whom  we  are  indebted  for  a  more  thorough 
study  of  this  substance,  looks  upon  the  antiseptic  powers  of  tannic 
acid  as  that  property  which  would  suffice  to  play  an  important 
part  in  the  plant  economy.  This  suggestion  is  highly  inter- 
esting and  is  worthy  of  further  investigation.  Concerning  my 
own  investigations  with  regard  to  the  physiological  significance  of 
tannin3!  came  to  the  conclusion  that  tannin  is  erratic;  for  ex- 
ample, in  summer  it  wanders  from  above  downward  in  the  bark 
and  vascular  system  of  the  stem  of  Quercus  pedunculata  ;  also  that 
it  stands  in  a  genetic  relation  to  the  formation  of  albuminoids. 


IY.    THE   CELL- WALL. 

As  soon  as  the  plant  anatomist  has  progressed  somewhat  in  his 
work  he  will  observe  the  significance  of  one  of  the  points  touched 
upon  in  this  chapter,  namely,  the  growth  in  thickness  and  surface 
of  the  cell-wall.  The  most  important  forms  of  cells  are  the  result  of 
localized  or  uniform  growth  in  thickness  of  the  cell-wall.  Upon 
the  growth  in  surface  depends  in  general  the  size  as  well  as  form 
of  every  plant-cell  and  therefore  every  plant-organ.  We  will  first 
treat  of  the  internal  structure  and  manner  of  growth  of  the  cell- 
wall,  then  of  its  chemistry,  and  finally  in  a  special  chapter,  of  the 
growth-products  of  the  cell-wall. 


1  Physiologic,  I.  306. 

2  Grundlinieii  zu  einer  Physiologic  des  Gerbstoffes.     Leipzig  1888. 

3  Sitzuugsberichte  der  Berliner  Akadeinie,  1885,  1887. 


26  COMPENDIUM  OF  GENERAL  BOTANY. 

A.  INTERNAL  STRUCTURE  AND  METHOD  OF  GROWTH  OF  THE 

CELL-WALL. 

The  mature  cell-wall  shows  two  internal  forms  of  structure, 
stratification  and  striation.  Both,  in  so  far  as  they  may  be  included 
here,1  are  usually  the  result  of  the  deposition  of  layers  containing 
successively  more  and  less  water,  or  (in  stratification)  they  may 
sometimes  be  due  to  chemical  differences  in  the  substances.  In 
stratification  we  are  concerned  with  concentric  layers  which  extend 
parallel  to  the  surface  of  the  cell-wall ;  in  striation,  with  lamellae 
which  usually  extend  radially.  Viewed  from  the  outside  these  stria- 
tions  seem  to  extend  either  diagonally  or  at  right  angles  to  the  cell- 
surface.  The  cell-wall  may  consist  of  longitudinal,  spiral,  or  annular 
lamellae,  and  these  rings  may  be  placed  diagonally  or  horizon- 
tally. 

The  upper  end  of  Fig.  11,  B,  shows  the  spiral  striations  of  a  cell 
cut  across.     The  lamellae  seem  to  be  radially  placed  ;  the  lower  end 
B          shows  the  diagonal  course  of  the  striation  when 
viewed  from  the  inner  surface.     Stratification 
and  striation  mark  the  cell-wall   into    numer- 
ous delicate  divisions.     The  various  layers  or 
complexes  of   layers   are   sometimes   so  com- 
bined  in   the   same  cell  as   to  cause  striation 
in  various  directions.     That  the  difference  in 
F      n  the  amount  of  water  present  is  the  cause  of 

A,   lameiiation   of   ceil-  stratification   and  striation  is  denied  by  some 

membrane;  B,  stratification         .,  m,  ,u  .     ,    .        .-,  .,  .    , 

of  ceii-membrane.  authors.     These   authors   maintain  that  thick- 

enings in  the  cell-wall  produce  striation  and  that  "contact  lines" 
cause  stratification  and  striation.  We  will,  however,  follow  CORRENS,* 
who  has  made  a  critical  study  of  this  subject  and  more  recently 
has  verified  his  former  opinions.  According  to  this  author  strati- 
fication and  striation  (in  the  true  sense)  are  usually  due  to  water 
differences,  and  sometimes  to  chemical  differences  in  cell-wall  sub- 
stances (having  different  refractive  indices).  The  same  questions 


1  Delicate  spiral  thickenings,  as  they  occur  in  cells  of  conifers,  and  membrane 
foldings  which  produce  longitudinal  striation  in  certain  epidermal  cells,  do  not 
belong  to  these  internal  structural  changes. 

2  CORRENS,  who  should  perhaps  be  considered  the  last  pupil  of  NAGELI,  wrote: 
"Zur  Kenntnis  der  innern   Struktur  der  veg.  Zellmembranen."    Pringsheim's 
Jahrbucher,  XXIII  (1891). 


TEE  CELL.  27 

which  are  to  be  considered  in  regard  to  the  structure  and  growth 
of  starch -grains  also  apply  to  the  cell-wall.  Excessive  drying  of  the 
cell-wall  causes  the  stratification  to  become  indistinct  or  to  disappear 
entirely,  but  it  will  reappear  on  the  absorption — imbibition — of 
water.  This  proves  that  the  stratification  of  cell-walls  depends 
upon  differences  in  the  amount  of  water.  The  same  is  true  in 
regard  to  striation.  Stratification  also  disappears  when  an  excessive 
amount  of  water  is  taken  up  by  imbibition. 

NAGELI  applied  his  theory  of  growth  by  intussusception  to 
the  stratification  of  starch-grains  and  cell-walls.  The  opposition 
to  this  theory  still  continues  :  scholars  are  divided  into  two 
distinct  groups.  Although  Nageli's  work  in  regard  to  starch- 
grains  is  one  of  the  greatest  and  most  important  productions  in 
botanical  science,  yet  the  fact  remains  that  the  process  of  apposition, 
at  least  in  regard  to  the  growth  of  cell-walls,  is  of  a  wider  applica- 
tion than  Nageli's  theory  would  seem  to  permit.  A  refutation  of 
the  theory  of  intussusception  is  nevertheless  out  of  the  question. 

According  to  the  theory  of  intussusception  the  starch-grain 
within  the  cell  increases  in  size  at  the  expense  of  the  soluble  starch 
substance  entering  through  the  cell-wall  from  without,  assisted  by 
the  living  plasm  of  the  cell.  The  cell-wall  receives  its  building 
material  direct  from  the  primordial  utricle.  The  apposition  theory 
teaches  that  the  strata  are  formed  by  superposition,  always  on 
the  outer  surface  of  the  starch-grain,  and  on  the  inner  surface 
of  the  cell-wall.  There  is  no  doubt  that  the  lamellae  of  the  cell-wall 
are  frequently  formed  by  apposition,  but  the  growth  of  such  lamellce 
is  evidence  that  their  increase  in  thickness  takes  place  internally, 
and  not  on  the  surface.  In  proof  of  this  there  are  certain  facts 
concerning  development  to  be  mentioned  below.  Such  facts,  how- 
ever, are  also  evidence  of  surface  growth  by  intussusception.  I  will 
limit  myself  to  the  following  statements. 

The  development  of  the  algal  group  Glceocapsa  gives  additional 
evidence  in  favor  of  the  growth  in  thickness  and  surface  of  cell-wall 
according  to  the  theory  of  intussusception  (NlGELi,1  CoBRENS2). 
The  outer  cell- wall  grows  in  thickness  and  in  surface  until  it  has 
increased  219  times  its  original  volume  without  being  in  direct  con- 
tact with  the  cell-plasm.  Although  this  example  holds  true  for 


1  Starkekorner. 

2  Flora,  1889.     Also  WILLE'S  contributions  in  defence  of  the  theory  of  intussus- 
ception (Christiania,  1886). 


28 


COMPENDIUM  OF  GENERAL  BOTANY. 


growth  in  thickness  as  well  as  in  surface,  yet  the  following  considera- 
tions are  opposed  to  a  surface  growth  by  apposition.  According  to 
KRABBE  1  considerable  growth  in  surface  may  be  noticed  in  lamellse 
•of  various  bast  cells  which  are  not  in  direct  contact  with  the  cell- 
plasm.  Further,  there  may  occur  cell-wall  foldings  which  evi- 
dently are  (ZIMMERMANN,  KNY)  formed  in  direct  opposition  to  the 
hydrostatic  pressure  of  the  cell  ;  therefore  their  growth  cannot  be 
the  result  of  expansion  through  hydrostatic  pressure.2  (This  will 
again  be  referred  to  in  the  chapter  on  the  physiology  of  growth.) 

The  very  frequent  spiral  arrangement  of  the  molecules  of  cylin- 
drical cells  is  also  evidence  in  favor  of  the  theory  of  internal  pro- 

cesses of  growth  ;  this  apparent  twisting  of 
the  cell  upon  its  axis  is  more  easily  explained 
by  growth  processes  within  the  interior  of 
the  cell-wall  than  by  processes  of  apposition- 
Phenomena  of  tension  which  become  mani- 
fest when  starch-grains  are  partially  cut  also 
point  to  internal  differentiations. 

According  to  the  investigations  of 
SCHMITZ,  STRASBURGER,  and  NOLL  on  the 
one  hand,  and  KEINHARDT  on  the  other, 
the  following  statement  in  regard  to  surface- 
growth  of  the  cell-  wall  will  hold  good,  and 
wil1  not  be  contradictory  to  what  has  been 

said  before-  ^ew  la^ers  are  without  doubt 

n-ffpl)  rJpnnsifprl  hv  thp  rmmnrrlial  nfn'plp 
°Jien  (  DJ  Tn€'  Pri 

while  surface  growth  is  going  on;  the  outer 
and  older  layers  are  thereby  passively  ex- 

panded and  ruptured.  These  layers  very  probably  grow  in  surface  by 
intercalation  (intussusception).  Such  formation  of  new  lamellae  must 
not  of  necessity  always  take  place.  According  to  REINHARDT'SS 
investigations  it  is  not  demonstrable  in  hyphal  fungi  (Peziza). 

The  following  interesting  observation  will  aid  one  in  judging 
the  "theory  of  expansion  "  more  critically.  The  advancing  tips  of 
growing  cells  (fungal  hyphse)  were  observed  directly,  By  the  aid 
of  adhering  granules  it  was  noticed  that  the  increase  in  surface  was 
at  a  maximum  at  the  place  of  greatest  curvature,  and  extended  only 


III.  Eight-celled  colony  of  Gloeo- 
capsa  alpina,  Nag.   (X  500.   After 


1  Pringsheim's  Jahrbucher,  XVIII  (1887). 

2  Supposition  of  the  defenders  of  the  apposition  theory. 

3  Pringsheim's  Jahrbilcher,  XXIII  (1892). 


THE  CELL.  29 

a  short  distance  below  this.  The  growing  surface  consists  approxi- 
mately of  the  hemispherical  apex,  with  an  additional  cylindrical 
portion  equal  in  height  to  the  radius  of  the  hemisphere.  Under 
certain  conditions  rupturing  of  the  hyphae  with  extrusion  of  plasm 
takes  place.  This  rupturing,  however,  does  not  take  place  at  the 
point  of  greatest  curvature  and  maximum  growth  in  the  apical  area, 
but  usually  at  that  point  below  the  tip  where  the  cell-wall  has  ac- 
quired its  greatest  thickness,  hence  at  the  base  of  the  growing  part. 
The  apposition  theory,  which  teaches  that  inner  lamellae  or  layers  are 
formed  by  apposition  and  outer  ones  are  ruptured  by  expansion, 
would  only  permit  rupture  of  the  cell-membrane  at  the  place  of 
maximum  growth,  that  is,  in  the  region  of  maximum  curvature, 
which  is  not  the  case.  Rupturing  takes  place  at  the  points  of  greatest 
tangential  tension  because  of  the  hydrostatic  pressure,  not  at  the 
points  of  supposed  greatest  expansion.  According  to  Reinhardfs 
assumption  apical  growth  of  the  cell  takes  place  in  such  a  manner 
that  given  points  lying  nearest  the  axis  at  the  apical  area  form  tra- 
jectural  curves  outward  with  the  advance  (growth)  of  the  apex. 

The  theory  of  intussusception  is  based  upon  deeper  and  more 
far-reaching  considerations  underlying  the  sphere  of  molecular 
physics  as  opposed  to  the  more  crude  theory  of  apposition.  As  al- 
ready indicated,  the  latter  theory  presupposes  considerable  mechani- 
cal expansion  for  the  surface  growth  of  cell-membranes.  Let  us 
follow  Nageli's  '  arguments  more  closely.  The  cylindrical  cells  of 
the  alga  Spirogyra  grow  considerably  in  length  while  retaining 
nearly  the  same  thickness.  Intussusception  requires  only  an  infi- 
nitely small  reduction  in  the  cohesion  of  molecules  in  the  longitu- 
dinal direction  to  make  it  possible  for  new  molecules  to  be 
intercalated.  Tension  is  thus  equalized,  to  be  again  disturbed  by 
the  same  infinitely  small  difference. 

No  difference  can  ~be  demonstrated  in  molecular  cohesion  in  a 
longitudinal  or  transverse  direction  of  the  cell-wall.  According  to 
the  apposition  theory  the  difference  in  cohesion  in  the  two  direc- 
tions must  be  very  great,  because  it  presupposes  that  layers  must  be 
torn  apart  in  a  longitudinal  direction.  The  intussusception  theory 
also  postulates  a  very  slight  diminution  in  tension  in  a  longitudinal 
direction. 

Before  dismissing  this  difficult  subject  it  should  be  noted  that 


1  Starkekorner,  page  279  et  seq. 


30  COMPENDIUM  OF  GENERAL  BOTANY. 

Nageli  in  answering  the  how  of  starcli  and  cell- wall  growth  accord- 
ing to  the  intussusception  theory  expressly  omits  i\\ewhy  of  cell-wall 
growth.  To  find  the  causes  for  this  why  is  impossible  according  to 
his  own  statement  because  of  the  lack  of  knowledge  in  regard  to 
molecular  cohesion,  tension  in  various  directions,  distribution  of 
water  and  cell-wall  substance,  etc.  In  starch-grains  a  similar  dif- 
ficulty is  met  with,  namely,  the  phenomenon  of  the  smallest  par- 
ticles (micellae)  surrounding  themselves  with  a  layer  of  water  of 
definite  thickness.  This  also  depends  upon  molecular  forces  "whose 
nature  is  unknown." 

B.  CHEMICAL  COMPOSITION  AND  SECONDARY  CHANGES  IN  THE 

CELL- WALL. 

The  cell-wall  is  the  product  of  living  protoplasm  ;  that  is,  a  car- 
bohydrate is  produced  from  an  albuminoid.  The  details  of  this 
chemical  process  are  unknown. 

The  wall  of  young  cells  consists  principally  of  cellulose.  Its  form 
ula,  similar  to  that  of  starch,  is  given  as  n  (C6H10O5).  Its  molecular 
weight  is  therefore  unknown.  Of  the  microchemical  reactions  the 
following  may  be  mentioned :  swelling  and  final  solution  in  con- 
centrated sulphuric  acid,  in  chromic  acid,  and  arnmoniacal  oxide  of 
copper;  blue  coloration  wTith  a  solution  of  iodine,  dilute  sulphuric 
acid,  and  chlor-zinc-iodine.  The  cellulose  of  fungi  is  a  modification 
of  cellulose  which  shows  these  reactions  only  after  having  been 
treated  for  weeks  with  KHO.  Before  being  so  treated  it  gives  a 
yellowish  or  brown  reaction  with  iodine  and  sulphuric  acid  ;  it  is 
also  less  affected  by  acids.  Another  modification  is  the  "  reserve 
celluloss,"  which  will  receive  only  brief  mention. 

Very  frequently  cellulose  undergoes  a  change  in  composition, 
either  throughout  its  entire  thickness  or  only  in  certain  layers  or 
areas.  The  following  are  the  most  important  forms  of  changes  oc- 
curring in  the  cell-wall  substance  :  (a)  corky,  (5)  ligneous,  (c)  muci- 
laginous, (d)  deposition  of  coloring  material  and  inorganic  com- 
pounds (mineral  matter).  Our  knowledge  concerning  these  is  to  a 
certain  extent  very  imperfect. 

(a)  In  a  later  discussion  upon  protection  against  loss  of  water 
(epidermal  system)  the  value  of  corky  cell-walls  will  become  more 
apparent.  The  most  useful  property  of  corky  or  "  cuticularized" 
(suberized)  membranes  is  the  great,  though  not  absolute,  imper- 


THE  CELL.  31 

meability  to  water.  A  fatty  substance  called  "  suberin  "  (HOHNEL) 
(cutin)  is  contained  in  the  cell-walls  thus  changed.  Concentrated 
sulphuric  acid  does  not  dissolve  corky  cell-walls.  Continued  boil- 
ing with  "  Schulze's  mixture,"  that  is,  chloride  of  potassium  and 
sulphuric  acid  (caution  ! ),  causes  the  suberized  membranes  to  form 
into  oily  drops  of  eerie  acid.  These  corky  membranes  are  widely  dis- 
tributed. The  teleological  explanation  of  this  is  that  cells  exposed 
to  the  air  require  such  membranes  to  guard  against  excessive  evap- 
oration. Examples:  epidermal  cells,  pollen-grains,  spores,  etc.  In 
connection  with  the  epidermal  tissue  we  will  refer  to  the  waxy 
deposits  on  the  outer  surface  of  the  cell-wall.  (Great  extensibility 
is  not  characteristic  of  corky  cellulose  membranes,  as  is  frequently 
maintained.) 

(b)  Lignification  cannot  be  satisfactorily  explained  at  present. 
Microchemistry   and   analytical    chemistry    have    explained    many 
things,    but   have    failed    to    explain    definitely    what   lignification 
is  or  what  function  it  serves.     A  well-known   reaction   of  woody 
membranes  is  a  red   coloration  with   phloroglucin  and  hydrochloric 
acid.      Anilin  sulphate  colors  them    yellow ;    phenol   with  hydro- 
chloric acid  stains  them  green  to  blue.     Woody  membranes  resist 
the  action  of  sulphuric  acid  more  than  cellulose  and  less  than  corky 
membranes ;  with  iodine  and   sulphuric  acid  they  turn  yellow   or 
yellowish    brown.      After  treatment  with    potassium    hydrate  the 
above-mentioned  cellulose  reaction  (blue  coloration  similar  to  that  of 
fungus  cellulose)  appears.     The  chemical  nature  of  woody  cell-walls 
has   been   studied   by  various  authors,  among  whom  are  HOHNEL, 
SINGER,  and    NICKEL.      The   red   reaction    with    phloroglucin    and 
hydrochloric  acid  is  probably  due  to  two  substances,  coniferin  (lig- 
nin)  and  vanillin.     NAGELI  believed  the  chief  cause  of  lignification, 
to  be  a  deposition  of  mineral   salts  (lime  salts).     The  physical  prop- 
erties of  woody  cell-walls  also  require  further  study. 

(c)  There  is  a  modification  of  the  cell-membrane  remarkable  for 
its  power  of  absorbing  large  quantities  of  water  with  considerable  in- 
crease in  volume ;  in  the  dry  state  it  is  hard  and  brittle,  when  filled 
with  water  it  is  mucilaginous,  hence  the  designation  mucilaginous 
cells.    We  are  here  concerned  with  various  gums  and  plant  mucilages, 
some  of  which   give  a  cellulose  reaction  with  iodine  and  sulphuric 
acid,  while  others  do  not.     Such  membranes  serve  to  retain  the  mois- 
ture for  the  plant.      Medicine  utilizes  the  mucilaginous  products  of 
various  plants.     Of  these  may  be  mentioned  the  gelatinous  stalks  of 


32  COMPENDIUM  OF  GENERAL  BOTANY. 

Laminaria,  the  gummy  exudation  from  Astragalus  gummifer,  seeds 
of  'Linum,  Gummi  arabicum  from  the  bark  of  Acacia  Senegal,  and 
other  species,  roots  and  leaves  of  Althaece,  and  the  gelatin  of  marine 
algae.  The  membranes  of  entire  cell-complexes  often  become 
mucilaginous  (tragacanth  gum).  What  has  been  stated  in  regard 
to  the  mucilage  of  orchid-bulbs  indicates  that  mucilage  may  be 
produced  within  the  cell,  hence  is  not  always  of  membranous 
origin.1 

(d)  Yarious  coloring  materials  are  deposited  in  cell-walls  of 
different  plants :  santalin  in  red  sandalwood,  haematoxylin  in  the 
blue  campeche-wood,  brasiliri  in  red-wood,  morin  in  yellow- 
wood,  etc.  In  all  these  cases,  as  also  in  the  well-known  ebony 
(Diospyros  Ebenum\  we  are  concerned  with  a  transition  from  phloem 
(Splint)  into  heart-wood  (kernholz) ;  or  in  other  words  a  deposition 
of  coloring  substances -and  tannin  in  the  originally  colorless  cellulose 
membrane.  Cell-walls  containing  silica  and  carbonate  of  lime  have 
been  known  for  a  long  time  ;  the  former  among  Equisetce  and 
Graminece.  Burning  such  silica-bearing  plants  after  treating  with 
sulphuric  acid  leaves  a  "skeleton."  This  skeleton  consists  not  only 
of  SiO2,  but  usually  also  of  salts  of  K,  Ca,  and  Mg.  The  silicious 
membranes  of  the  small  cells  in  the  epidermis  of  many  grasses 
(dwarf-cells)  serve  as  a  protection  against  destruction  by  snails 
(STAHL).  Incrustation  of  cell-walls  with  calcium  carbonate  has  been 
observed  in  the  hair-cells  of  phanerogams  (Composite,  Borraginece) ; 
calcium  oxalate  occurs  in  cell-walls  of  conifers.  Those  peculiar 
excrescences  of  the  cell-wall  extending  into  the  cell-lumen  (Ficus, 
Acanthacece)  containing  calcium  carbonate  and  known  as  "  cysto- 
liths  "  also  belong  here.  According  to  HABERLANDT  the  calcium 
carbonate  contained  in  the  cystoliths  of  Ficus  Carica  (leaf)  is  ulti- 
mately redissolved  and  utilized  in  the  metabolic  processes  of  the 
plant. 

C.  PRODUCTS  OF  THE  GROWTH  IN  THICKNESS  AND  SURFACE  OF 
THE  CELL-WALLS. 

We  must  distinguish  the  uniform  growth  in  surface  and  thick- 
ness of  the  cell-walls  from  the  not  less  frequent  and  especially  im- 
portant localised  growth.  We  have  already  touched  upon  that 


FRANK'S  Physiologic  gives  a  more  detailed  summary. 


THE  CELL.  33 

localized  surface  growth  which  causes  the  apical  growth  of  a  cell, 
and  will  now  treat  principally  of  growth  in  thickness. 
As  to  development  two  forms  can  be  recognized  : 

(a)  At  points  of  active  cell-formation  (ineristem  of  apical  areas) 
division  proceeds  so  rapidly  and  the  growth  in  thickness  of  cell- 
walls  is  so  slight  and  so  soon  completed  that  all  membranes  have 
nearly  the  same  immeasurable  thinness.     Only  after  cell-formation 
ceases  or  becomes  less  frequent,  that  is,  at  some  distance  from  the 
apical  area,  does  the  characteristic  thickening  of  cell-walls  begin. 

(b)  Less  commonly  growth  in  thickness  begins   and  continues 
immediately  after  the  formation  of  the  cell.     In  these  cases  the  rela- 
tive age  of  the  cell-wall  can  be  estimated  by  its  thickness  (examples : 
algal  threads  and  cork-formation). 

As  has  been  stated,  growth  in  thickness  may  be  uniform  and 
may  show  all  gradations  from  minimum  to  maximum,  that  is,  up  to 
total  occlusion  of  the  cell-lumen  (Fig.  13,  <z,  5,  <?). 


Of  the  very  frequent  unequal  cell-wall  thickening  I  will  men- 
tion first  the  u  collenchymatous."  Cells  showing  this  thickening 
belong  to  the  mechanical  tissues  and  are  characterized  by  thick 
angles  (Fig.  14).  The  selection  of  the  name  "  collenchyma " 
(^o^Atf,  lime)  probably  depends  upon  the  fact 
that  certain  cells  with  walls  of  unequal  thickness 
and  at  the  same  time  gelatinous  were  so  named. 
Collenchyma  is,  however,  not  capable  of  swelling 
to  any  considerable  extent  (AMBRONN). 

The  other  forms  of  localized  growth  in  thick- 
ness of  cell-walls  may  be  grouped  as  follows  :  FIG.  14. 

I.  Spine  or  wart-like  thickenings  (usually  projecting  outward). 

II.  Linear  or  fibrous  thickenings  (usually  projecting  inward). 

III.  "Porous"  thickenings;   that  is,  thickenings  with  the  ex- 
ception of  certain  areas  called  "  pores." 


34 


COMPENDIUM  OF  GENERAL  BOTANY. 


The  following  considerations  will  be  of  interest  more  especially 
from  the  physiological  point  of  view  : 

I.  This  form  of  cell-wall  thickening  is  usually  met  with  in  iso- 
lated cells  whether  they  are   bounded  by  air   or  water.     In   the 
atmosphere  we   find   the   spores   of   cryptogams,  pollen-grains   of 
phanerogams;    in  water    the  unicellular    algae.      The   thickenings 
evidently  serve  definite  purposes,  some  of  which  are  as  yet  not  made 
clear.     The  spines  of  pollen-grains  assist  in  adhering  to  the  stigma 
where  the  formation  of  the  pollen-tube  begins ;  spines  of  spores  no 
doubt  serve  the  purpose  of  fastening  them  to  the  soil  or  other  sub- 
stratum.    They  also  favor  the  transportation  of  pollen-grains  by 
insects. 

II.  Linear   thickenings    are   of    the   greatest  importance   for 
certain  life-functions  of  the  more  highly  organized  plants.      The 
remaining  portion  of  the  cell-wall  of  such  elements  is  usually  very 
thin.     The  thickenings  serve  as  mechanical  support  against  radial 
pressure.     To  understand  their  use  it  is  necessary  to  be  somewhat 
more  explicit.     The  figures  (Fig.  15)  give  a  fair  idea  of  the  external 
appearance  of  these  elements  and  require  but  little  explanation.    They 
represent  portions  of  vessels.     By  vessel  is  meant  a  row  of  cells 


FIG.  15. — Schematic  lateral  view  of  various  vascular  forms. 

In  a  and  6  the  proximal  surface  is  supposed  to  be  removed,  showing  the  distal  halves  of  the 
rings  with  their  cut  ends. 

converted  into  a  tube,  having  characteristic  cell- wall  thickenings 
and  being  essentially  a  lifeless  structure.  They  are  formed  by 
the  partial  or  total  absorption  of  the  transverse  partitions  of  cell- 


THE  CELL.  35 

rows.  They  are  lifeless  because  they  no  longer  possess  a  primordial 
utricle.  It  is  these  vessels  that  are  characterized  by  the  thickenings 
under  discussion. 

The  designation  annular  (ring)  and  spiral  vessels  for  a  and  &, 
and  reticulated,  scalariform,  and  porous  (pitted),  for  <?,  d,  and  <?,  need 
no  further  explanation.  The  five  forms  represent  mechanically  sup- 
ported tubes  serving  the  purpose  of  conducting  water  in  the  plant- 
body.  Why  mechanically  supported?  Because  they  are  contigu- 
ous with  living  cells, and  these  living  cells  are  capable  of  exerting  a- 
high  hydrostatic  pressure,  and  actually  force  water  through  thin  por- 
tions of  the  cell- walls  into  the  vessels ;  otherwise  they  would  be  com- 
pressed by  the  living  cells,  since  they  are  not  capable  of  exerting  any 
active  pressure  themselves.  Such  is  the  purpose  of  the  thickenings 
described.  Further,  it  is  known  that  vessels  contain  alternately  air 
and  water,  and  that  when  branches  are  cut  under  mercury  or  colored 
liquids  the  vessels  become  filled  to  a  given  height  with  these  liquids. 
(This  is  also  true  of  mercury  in  spite  of  its  capillary  depression.) 
Therefore  there  is  at  times  a  negative  pressure  within  the  vessels, 
which  again  necessitates  mechanical  support.  The  structural  rela- 
tions are  thus  teleologically  explained.  Annular  and  spiral  *  vessels 
on  the  one  hand,  and  reticulate,  scalariform,  and  porous  (pitted) 
vessels  on  the  other,  differ  very  materially  in  one  respect.  This 
difference  may  be  indicated  by  the  designation  primary  (a  and  b) 
and  secondary  (<?,  rf,  e).  The  following  will  serve  to  explain  it. 

In  general  only  thin  portions  of  cell-walls  are  capable  of  growth. 
From  this  it  follows  that  annular  elements  are  given  considerable 
scope  for  growth  in  length  by  the  localized  surface-growth  between 
the  rings  thus  forcing  them  farther  apart.  Also  the  spirally  thick- 
ened elements,  whose  spirals  are  at  first  closely  wound,  grow  at  the 
thinner  portions,  causing  the  spirals  to  become  more  slanting.  An- 
nular and  spiral  vessels  stretch  in  a  longitudinal  direction.  Such 
growth  of  thin-walled  portions,  accompanied  by  elongation  of  the 
entire  element,  cannot  take  place  in  the  vessel-forms  #,  d,  and  e  be- 
cause of  the  firmly  adhering  longitudinal  thickenings.  This  again 
explains  from  a  teleological  standpoint  why  a  plant-organ  contains  or 
develops  annular  and  spiral  vascular  elements  during  the  period  of 
growth,  and  that  during  the  second  period,  that  is,  when  growth  in 
length  has  ceased,  the  secondary  non-elongating  vessels  are  more 


1  The  German  expression  "  Schraubengefiiss  "  (screw-vessel)  is  more  correct. — 
TRANS. 


36  COMPENDIUM  OF  GENERAL  BOTANY. 

suitable.  In  passing  it  should  be  noted  that  spiral  vessels  often  con- 
tain a  number  of  parallel  fibres  (sometimes  as  many  as  twenty);  also 
that  spirals  as  shown  at  5  (Fig.  15)  are  designated  as  sinistrorse  in 
botanical  terminology  (beginning  at  the  side  facing  the  observer 
they  extend  upward  from  left  to  right). 

The  tracheids  of  insects  and  the  vessels  of  plants  are  formed 
upon  similar  physiological  principles. 

So  far  only  the  surface  view  of  the  thickened  walls  of  secondary 
vessels  (<?,  d,  e)  has  been  presented,  in  order  to  avoid  confusion. 
The  view,  corresponding  to  the  outermost  surface  (^highest  focus 
of  the  microscope),  does  not  show  us  the  entire  structure  of  these 
organs.  In  III  we  will  study  the  profile  view  of  these  vessels 
(hence  cross-sections). 

There  are  a  number  of  special  cases  belonging  to  the  category  of 
fibrous  and  linear  thickenings.  For  the  most  part  these  will  be 
referred  to  in  the  discussion  of  special  structures  of  tissues  and  in 
the  chapter  on  reproduction.  Here  will  be  mentioned  only  the 
thickenings  of  the  guard-cells  of  stomata  and  the  membrane-thick- 
enings of  the  dynamically  active  cells  which  cause  the  opening  of 
anthers.  Two  isolated  instances  may  yet  be  mentioned  as  belonging 
here :  the  thick  pillars  in  palisade-cells  of  Cycas  leaves,  which  very 
probably  serve  as  a  protection  against  longitudinal  pressure  during 
dry  periods  ;  and  the  cellulose  projections  from  the  inner  surface  of 
the  cell-wall  of  the  marine  alga  Caulerpa,  which  apparently  serve  to 
prevent  the  collapse  of  the  cell,  since  no  septae  are  present. 

III.  "  Porous  thickening "  sounds  almost  paradoxical,  yet  we 
will  use  this  expression  to  designate  that  form  of  growth  in  thick- 
ness which  affects  the  entire  cell-wall  with  the  exception  of  very 
small  circumscribed  areas.  These  small  areas  which  remain  thin 
are  called  pores  (pits).  The  term  pore  in  plant  anatomy,  therefore, 
does  not  mean  an  opening  through  the  cell-wall,  but  an  area  which 
has  remained  thin. 

Physiological  considerations  will  explain  in  general  the  uses  of 
such  formations  (see  Fig.  16).  The  interchange  of  fluids  from  cell 
to  cell  (living  cells)  takes  place  primarily  through  the  primordial 
utricle ;  also  through  the  cell-wall,  the  dialyzing  resistance  of  the 
same  being  less  in  proportion  to  its  thinness,  other  things  being 
equal.  This  latter  is  true  of  both  living  and  dead  cells. — I  may  state 
here  that  more  recent  investigations  have  demonstrated  very  delicate 
plasmic  connections  between  cells  (TANGL,  MOORE,  GARDINER,  Rus- 


THE  CELL.  37 

sow,  STKASBURGER,  and  others).  Upon  these  discoveries  future 
investigators  may  base  important  conclusions  of  a  widely  different 
nature;  as,  for  example,  the  transmission  of  irritability.  This  will 
not,  however,  be  further  mentioned  at  this  point ;  we  will  main- 
tain that  pores  facilitate  the  interchange  of  fluids  from  cell  to  cell, 
as  well  as  between  cell  and  vessel  (tracheid). 

These  pores  or  thin  cell-wall  areas  are  often  of  circular  or  oval 
form,  again  linear  or  simply  fissure-like.  The  accompanying  figure 
represents  various  forms  of  ordinary  pores. 

a,  shows  fissure-like  pores ;  &,  right-hand  side,  shows  rounded 
and  oval  pores,  all  in  surface  view;  Z>,  left  side,  shows  the  corre- 
sponding pores  in  profile,  that  is,  in  ver- 
tical  section  through  the  cell-wall.  Here 
the  pore  is  shown  to  be  a  canal.  It  may 
be  stated  that  as  the  rule  pores  of  neigh- 
boring cells  meet  each  other  ;  to  this  there 
are  exceptions.1  It  is  also  the  rule  that  a 
these  canals  pass  through  the  cell-wall  at 
right  angles.  Upon  the  number  of  pores  in  a  given  cell-wall  area 
the  prevailing  direction  of  the  interchange  of  food  materials  may 
be  based.  Without  further  elucidation  it  is  evident  that  thin- 
walled  cells  (  for  example,  most  assimilating  cells)  do  not  require 
pores,  though  there  is  extensive  interchange  of  food-substances 
between  them  and  other  cells. 

The  rounded  or  oval  pores  are  typical  in  those  moderately  thick- 
ened elements  which  function  chiefly  in  nutrition;  such  as  the  storing 
and  conducting  parenchyma  cells  of  pith  and  cortex,  the  storing  and 
conducting  cells  of  medullary  rays  and  wood-parenchyma.  These  will 
be  further  discussed  later.  The  above-named  \\\\ewc  fissure-like  pores 
are  characteristic  of  mechanical  cells.  It  is  evident  that  cells  which 
are  destined  to  withstand  pressure  or  tension  may  still  perform  this 
function  though  devoid  of  life,  since  the  dead  cell-wall  constitutes 
the  most  important  part.  The  pores  in  mature  mechanical  cells 
therefore  appear  to  be  harmful,  since  they  form  interruptions  in  the 
continuity  of  the  cell- wall  substance.  But  so  long  as  these  elements, 
which  later  subserve  a  purely  mechanical  function,  grow,  they  must 
be  nourished,  and  indeed  richly.  The  necessary  supply  of  cell-sap  is 


1  Such  cases  require  further  study.     In  advance  it  may  be  stated  that  their 
explanation  will  probably  throw  light  upon  new  adaptations. 


38 


COMPENDIUM  OF  GENERAL  BOTANY. 


facilitated  by  means  of  the  pores.  Secondarily  it  may  occur  that 
cell-sap  is  conducted  through  the  spiral  vessels  and  other  matured 
mechanical  cells  during  the  entire  life-period  of  the  plant.  In  such 
cases  pores  are  a  necessity  for  mechanical  cells.  Nevertheless  it  is 
evident  that  porosity  does  not  materially  interfere  with  the  proper 
function  of  such  cells.  In  typically  mechanical  cells  pores  are 
therefore  scarcely  noticeable.  As  a  rule  they  extend  diagonally, 
more  rarely  longitudinally. 

We  shall  now  consider  a  new  form  of  pore.  Pores  heretofore 
considered  (Fig.  16)  are  called  simple,  ordinary  or  uiibordered  pits 
or  pores.  This  new  form  of  pore  is  called  a  bordered  pore  or  pit. 

0 
0 
© 


FIG.  17. 

a  shows  a  bordered  pit  in  cross-section,  which  also  explains  the  appearance  in  surface  view 
as  shown  at  b. 

The  two  pore  canals  of  bordered  pits  meet  funnel-like,  that  is,  the 
two  large  thin  membranous  surfaces  come  in  contact.  This  mem- 
brane is  therefore  much  larger  than  the  diameter  of  the  pore-canal 
(see  Fig.  17,  a). 

Physiological  anatomy  still  has  here  an  opportunity  to  solve  an 
interesting  problem.  For  the  present  we  must  be  satisfied  with 
the  suggestions  of  the  greatest  tissue  physiologist,  SCHWENDENEK, 
in  regard  to  the  structure  of  these  bordered  pits.  Schwendener  sup- 
poses the  following  arrangement.  The  presence  of  a  large  thin 
membranous  area  to  facilitate  the  exchange  of  fluids  while  the 
cell  retains  the  greatest  possible  firmness.  This  seems  to  be  a 
very  rational  explanation.  However,  as  already  stated,  we  have  no 
exact  knowledge  of  the  function  of  these  structures.  Another 
hypothesis  (Russow)  supposes  an  arrangement  for  ventilation  which 
is  based  upon  the  presence  of  the  u  torus,"  that  is,  a  thickened 
central  portion  of  the  closing  membrane  (see  Fig.  17,  a).  This 
torus  may  be  forced  to  one  side  or  the  other  of  the  pore- 
canal  entrance  by  excessive  pressure.  Schwendener  succeeded  in 


THE  CELL.  39 

forcing  water  through  stoppers  of  wood  which  consisted  mainly  of 
tracheids  by  employing  considerable  pressure  (3-4  atmospheres), 
and  the  quantity  of  water  pressed  through  was  proportional  to  the 
pressure.  But  according  to  PAPPENHEIM'S  more  recent  investi- 
gations '  and  Russow's  earlier  observations  (1877)  a  pressure  of  one 
atmosphere  suffices  to  force  the  torus  against  the  pore  opening,  and 
the  amount  of  water  passed  through  is  thereby  reduced  (Pappenheim). 
GODLEWSKY  supposes  the  torus  to  function  similar  to  a  platinum 
cone  used  in  the  chemical  laboratory.  According  to  this  investi- 
gator the  margin  of  the  torus  is  crenated,  and  fine  radial  thickenings 
or  something  similar  are  supposed  to  extend  from  the  margin  of  the 
torus  over  the  margin  of  the  closing  membrane  (margo).  In  this 
way  the  margo  when  pressed  against  the  pit  cavity  acts  similarly  to 
a  folded  filter ;  the  crenated  margin  of  the  torus  prevents  the  tear- 
ing of  the  filter,  and  still  permits  the  passage  of  water.3 

Bordered  pits  are  therefore  all  those  thin  cell-wall  areas  of  the 
above-mentioned  secondary  vessels ;  consequently  not  only  of  porous 
vessels  but  also  of  reticular  and  scalariform  vessels.  Accordingly  a 
cross-section  or  profile  view  of  two  contiguous  cell-walls  of  a 
scalariform  vessel,  for  example,  would  appear  as  shown  in  Fig.  18.  A 
surface  view  of  the  same  pits  is  represented  at  the  right  in  the  figure. 

We  will  now  pass  to  the  localized  surface-growth  of  the  cell- 
wall.  We  have  already  become  familiar  with  one  instance  of 
the  elongation  of  annular  and 
spiral  vessels.  Another  in- 
stance is  to  be  observed  in 
cell-division  (rather  the  prep- 
aration to  divide)  of  the  alga 
group  Desmidiacece.  Their 
asexual  development  takes 
place  through  division.  Fig. 
19  explains  itself.  We  are 
here  concerned  with  the  zone 

U-    U      V  -          ^  •  £  F10-    18' 

which   lies    in   the    region   of 

the  constriction  of  the  cell ;    it  is  the  growing  zone.      After  the 

elongation  of  this  zone  a  septum  is  formed  in  its  middle  portion. 


1  Berichte  der  deutschen  botauischen  Gesellschaft,  1889. 

2  Russow's  communication  "  Zur  Kenntuis  des  Holzes,  etc.,"  is  to  be  found  in 
Bot.  Centmlblait,   XIII;    GODLEWSKY'S  communication  iu   Pringsheim's  Jahr- 
bilcher  fur  wissenschaftliche  Bot.,  XV  (1884). 


40 


COMPENDIUM  OF  GENERAL  BOTANY. 


A  frequently  discussed  example  (discovered  and  studied  by 
PKINGSHEIM)  is  the  growth  in  length  of  the  alga  Oedogonium. 
Here  we  are  not  concerned  simply  with  a  localized  surface  growth 


23  4 

FIG.  19. — Division  of  a  desmid-cell  (diagramatic). 

of  a  cylindrical  membranous  zone ;  the  complication  therein  lies  in 
the  fact  that  the  inner  layer  of  the  zone  is  undergoing  active  growth 
while  the  outer  layer  of  the  same  zone  becomes  torn  (Fig.  20). 

First  the  cellulose-ring  is  formed,  projecting  inward  (w).     The 
smaller  Fig.  20,  B,  represents  the  time-period  at  which  the  circular 
tearing  of  the  outer  membrane  has  taken  place 
(w'\  and  the  elongation  of  the  cell  takes  place 
at  the  expense  of  the  cellulose-ring.     After 
elongation  is  completed  a  new  septum  forms. 
Repetition  of  this  process  gives  rise  to  the 
"  caps  "  represented  in  the  larger  figure  (five 
caps  at  c  in  Fig.  A),  and  a  corresponding 
number  of  sheaths,  which  are  directed  upward, 
are  formed  by  the  projecting  edges  of  the 
repeatedly  ruptured  cell- wall.     These  sheaths 
are  just  separated  from  each  other,  and  each 
one  lies  in  the  vicinity  of  a  transverse  septum. 
Besides  the  instances  already  mentioned 
there   are   a   series   of   growth   phenomena 
belonging  to  this  category,  as  is  evident  from 
the  consideration  of  those  spongy  and  stellate 
tissues  in  leaves  and  water- 
plants.     Primarily  all  cells 
are  in  close  contact.     Three 
cells  may  enclose  an  inter- 
cellular  space   (i,  Fig  21), 
which  space  is  the  result  of 
peculiar    localized    surf  ace - 
growth  of  the  cell-membranes.1 

"We  have  been  obliged  to  mention  some  very  important  cell- 


FIG.  20.     (After  Sachs.) 


FIG.  21. 


1  Compare  ZIMMERMANN'S  Beitrage  zur  Morphologic  uud  Physiologic  dcr 
Pflanzenzelle,  Heft  3,  1893. 


THE  CELL.  41 

forms  in  this  section.  By  way  of  completion  we  will  add  some 
general  remarks  on  cell-forms  and  their  names,  since  the  expressions 
and  terms  concerned  pertain  to  the  most  valuable  language-treasure 
of  scientific  botany. 

The  terms  parenchyma  and  prosenchyma  have  long  been  es- 
tablished. They  do  not  refer  to  the  mode  of  growth,  but  simply 
to  the  form  of  the  cells.  The  term  parenchyma  is  used  to 
designate:  1,  all  isodiametric  and  tabular  cells  (hence  all  spherical, 
cubical,  parallelepipedal,  and  polygonal  cells) ;  2,  all  elongated 
cells  having  blunt  ends  (hence  all  elongated  cells  with  exactly  or 
.approximately  rectangular  ends).  All  elongated  cells  with  pointed 
or  sharp  endings  (hence  conical,  one  or  both  ends  blade-like) 
are  prosenchymatous.  The  most  important  representatives  of 
prosencfiyma  are  the  mechanical  cells  (skeleton-cells)  which  were 
named  "  sterome-cells  "  or  "  stereids  "  by  SCHWENDENEK. 

With  HABERLANDT  we  use  the  term  sclerenchyma  *  to  designate 
considerably  thickened  non-prosencTiymatous  elements  which  occur 
isolated  or  in  groups  in  various  tissues  exclusive  of  vascular  bundles; 
therefore  in  the  outer  cortex,  pith  (medulla),  etc.  Two  sclerenchyma- 
-cells  in  cross-section  are  shown  in  Fig.  22. 

A  fitting  introduction  to  a  brief  consideration  of  the  origin  of 
new  cells  is  the  statement  of  a  fact  which  sometimes  causes  difficul- 
ties to  the  beginner  in  phytotomy ;  it  is  that  every 
cell  has  a  membrane.  This  statement  holds  good 
for  every  tissue-structure.  On  maceration  (care- 
fully boiling,  for  example,  a  particle  of  wood  in 
sulphuric  acid  and  calcium  chloride)  the  tissue 
separates  into  its  individual  elements.  Even  an 
immeasurably  thin  wall  between  two  cells  of  a  Fm*  22' 
mature  tissue  is  thereby  split  and  shown  to  be  double.  The  macer- 
ating liquid  has  dissolved  the  cementing  material.  This  leads 
us  to  the  so-called  "  primary  membrane"  or  "  middle  lamella,"  which 
is,  however,  not  wholly  identical  with  the  intercellular  cement. 
The  prominent,  not  immeasurably  thin,  middle  lamella  of  woody 
cells  differs  from  the  remaining  membrane  in  having  a  different 
refractive  index.  Solubility  in  the  macerating  mixture  is  therefore 


JDE  BARY  (Comp.  Anatomy)  designates  typical  mechanical  cells  as  "  scleren- 
chyma  fibres";  hence  the  terminology  here  introduced  differs  markedly  from 
that  of  de  Bary. 


42  COMPENDIUM  OF  GENERAL  BOTANY. 

only  a  property  of  the  innermost  part  of  the  middle  lamella,  which 
part  DIPPEL  designated  as  the  middle  plate  or  intercellular  sub- 
stance. This  middle  plate  of  the  middle  lamella  is  common  to  two 
contiguous  cells ;  on  either  side  of  it  lies  the  outer  layer  of  the 
middle  lamella,  each  one  belonging  to  one  of  the  cells.  The  outer 
layer  of  the  middle  lamella  is  soluble  in  concentrated  H2S(X ,  while 
the  middle  lamella  is  not. 

Finally  we  will  mention  that,  similarly  to  the  middle  lamella 
of  the  outermost  surface  of  the  cell-wall,  the  surface  turned  toward 
the  primordial  utricle  is  also  lined  with  a  highly  refractive  thin 
membrane,  the  inner  membrane  of  WIESNER,  which  according  to 
this  author  is  rich  in  albuminoid  substances. 

It  has  been  discovered  recently  that  some  intercellular  spaces 
are  lined  with  plasmic  substances.  Whether  the  occurrence  of  this 
plasmic  substance  is  general  or  not  we  must  for  the  time  leave 
undecided. 

Y.  THE  OKIGIJST  OF  CELLS. 

Science  knows  no  other  method  for  the  origination  of  cells  than 
the  development  of  new  cells  from  pre-existing  ones.  The  first 
plants  which  existed  on  the  earth,  hence  also  the  first  plant-cells,  owe 
their  origin  to  a  command  of  the  Creator  issued  to  lifeless  matter  : 
"  Let  the  earth  bring  forth.  .  .  ."  The  Bible  and  science  complete 
each  other.  The  latter  answers  by  investigation  the  question  as  to 
the  method  of  the  origin  of  new  cells  from  pre-existing  ones.  It 
can  give  no  natural  method  for  the  origin  of  the  first  plant-cells.1 

There  are  various  ways  in  which  plants  may  form  new  cells 
from  pre-existing  ones.  Because  these  various  ways  are  sometimes 
not  sharply  defined,  it  is  at  once  evident  that  to  obtain  a  clear  idea 
of  what  does  take  place  it  is  necessary  to  discuss  typical  cases. 

We  distinguish  four  types  of  cell-formation,  as  follows  : 

I.   Cell-formation  *by  rejuvenescence,  or  direct  cell-formation. 
II.   Cell-formation  ~by  conjugation. 

III.  Free  cell-formation. 

IY.    Cell-formation  ~by  division  (meristematic). 

I,  II,  and  III  are  essentially  concerned  in  the  reproductive 
processes  of  plant-life,  that  is,  they  serve  to  propagate  the  individ- 

1  This  introductory  paragraph,  to  say  the  least,  is  very  unscientific.     It  does 
not  assist  the  advance  of  science. — TRANS. 


THE  CELL. 


ual  •  IV,  on  the  other  hand,  is  of  the  greatest  importance  in  the  veg- 
etative life  of  the  plant  (growth,  tissue-formation). 

I.  Direct  Cell-formation.  —  The  mother-cell,  with  its  entire  con- 
tents, excepting  the  membrane,  takes  part  in  the  formation  of  the 
daughter-cell.     The  life  of  the  mother-cell  passes  directly  into  that 
of  the  daughter-cell.     The  visible  phenomenon  connected  with  this 
process  is  the  contraction,  due  to  internal  forces,  of  the  primordial 
utricle  of  the  mother-cell,  and  the  subsequent  deposition  of  a  new 
cellulose  membrane  either  while  yet  within  the  old  membrane  or 
after  its  escape  from  the  same.     The  membrane  of  the  mother- 
cell  is  destroyed.     Example:   swarm-spore   formation  in   the  alga 
Stigeoclonium  insigne  (studied  by  NAGELT). 

II.  Conjugation.  —  The  contents  of  two  externally  not  dissimilar 
cells  unite  to  form  one  new  cell.     Either  the  contents  of  one  cell 
pass  into  the  lumen  of  the  other  cell  by 

means  of  outgrowths  from  the  membrane 
and  after  the  opening  of  the  contiguous 
membranous  areas,  or  the  contents  of  both 
cells  unite  by  moving  toward  each  other  and 
fusing.  The  united  cell-contents  are  then 
surrounded  by  a  new  membrane.  Ex- 
ample :  Spirogyra  and  similar  algae  (Fig. 
23). 

III.  Free     Cell  -formation.  —  The 
daughter-cells  appear  floating  in  the  con- 
tents of  the  mother-cell.     Small  particles 
are  differentiated  within  the  plasmic  con- 
tents  of    the    mother-cell    and    surround 

themselves  with  a  new  membrane.  This  process  is,  however,  con- 
nected with  nuclear  division.  Example  :  ascospore-formation  in 
asci  of  the  fungus-group  Ascomycetes.  In  this 
process  the  entire  plasmic  contents  of  the  mother- 
cell  are  not  utilized  (Fig.  24). 

IV.  Meristematic  Cell-formation  or  Cell-fo?*- 
mation  by  Division.  —  Septa   divide   the    entire 
contents  of  the  mother-cell.    Four  sub-groups  are 
recognizable. 
Asci  with        (a)  Splitting  up  of  the  plasm  with   complete 


FIG.  23. 

(After  Berthold  and  Landois.) 


FIG. 


and  Landois.)  (J)  Division  of  the  plasm  with  partial  mem- 

brane-formation which  occurs  simultaneously. 


44  COMPENDIUM  OF  GENERAL  BOTANY. 

(c)  Division   of   the   plasm   with  partial  membrane-formation 
which  occurs  subsequently. 

(d)  Cell-formation  by  budding. 

In  (a)  the  mother-cell  divides  into  two,  more  rarely  many, 
daughter-cells.  As  in  type  III  they  receive  a  complete  new  mem- 
brane, but  differ  in  that  the  entire  contents  of  the  mother-cell  are  util- 
ized. Example  :  spore-formation  among  certain  moulds  (Fig.  119). 

(J)  This  is  the  more  usual  form  of  cell-division  in  tissue-forma- 
tion. Internal  causes  bring  about  a  division  of  the  plasm  ;  then  sud- 
denly the  cellulose-membrane  makes  its  appearance,  usually  at  right 
angles  to  the  wall  of  the  mother-cell.  Hence  the  daughter-cells  possess 
in  part  the  membrane  of  the  mother-cell.  In  sharp  contradistinction 
to  (c)  no  intermediate  form  with  incomplete  septa  can  be  observed. 

(c)  The  primordial  utricle  becomes  constricted.     (In  cylindrical 
cells,  for  example,  there  appears  a  circular  fold.)     Finally,  when  this 
constriction  has  progressed  to  the  middle  point,  the  two  portions  sep- 
arate.    Immediately  following  this  process  the  cellulose- wall  begins 
to  form  from  without   inward,  sometimes  presenting  the   appear- 
ance of  a  constricting  membranous  fold  actively  encroaching  upon 
the  primordial  utricle.     But  the  cell-membrane  can  only  grow  by 
means  of  the  nourishing  plasm  ;  the  plasmic  constriction  is  therefore 
primary.     Example:  the  algal  genus  Spirogyra.     Since  such  divi- 
sion usually  occurs  in  darkness,  it  is  advisable  to  place  the  algae  in 
the  dark  before  examining  them ;  or  the  algae  may  be  selected  at 
iiight  and  placed  in  alcohol  to  be  examined  the  following  day.     By 
proper  management  all  intermediate  stages  of  cell-wall  formation 
may  be  found. 

(d)  Budding.     The  mother-cell  develops  a  bud  which  becomes 
independent  by  the  formation  of  a  septum.     The  bud  may  finally 

become  entirely  separated.  Example :  Sacharo- 
myces  cerevisice*  the  fungus  of  beer  fermentation 
(Fig.  25). 

Among  these  plants  (Sacharomyces)  the  inter- 
esting discovery  has  been  made  (REES)  that  they 
FIG.  25.  reproduce  differently  under  different  external  sur- 
roundings. In  the  usual  medium  (beer)  budding  is  the  prevailing 
mode  of  reproduction.  If  simply  kept  moist,  for  example,  upon 
slices  of  potato,  the  fungus  reproduces  by  free  cell-formation 
(ascospores).  Cell-formation  by  budding  is  also  typical  among 
the  Basidiomycetes. 


PAET  II. 
TISSUES    AND    SIMPLE    ORGANS. 


A.  STRUCTURE  OF  TISSUES  AND  SIMPLE  ORGANS. 

The  anatomist  distinguishes  between  formed  tissue,  we  permanent 
tissue,  and  tissue  in  the  process  of  formation,  or  formative  tissue. 
Formative  tissue — tissue  which  is  capable  of  growth  and  cell-division 
— is  in  general  designated  as  meristem.  Again,  a  distinction  is  made 
between  short-membered  parenchymatous  formative  tissue,  or  meri- 
stem in  the  narrower  sense,  and  longitudinally  extended  formative 
tissue  (more  prosenchymatous  in  nature),  or  cambium.  It  is  readily 
understood  that  every  cambial  tissue  is  more  or  less  secondary  in 
nature,  for  in  general  every  organ  begins  with  short  or  spherical 
cells  ("  primary  rneristem  "). 

By  an  organ  is  understood  a  cell  portion,  a  cell,  or  a  cell-complex, 
adapted  for  a  definite  function.  Tissue  is  a  purely  morphological 
conception.  Any  coherent  cell-complex  having  extension  in  at 
least  two  directions  may  be  designated  as  "  tissue."  The  considera- 
tion of  the  structure  of  organs  and  tissues  necessarily  coincides  with 
the  discussion  of  the  structure  of  the  plant  itself,  since  plants  are 
either  single  cellsi  cell-threads,  cell-surfaces,  or  cell-bodies* 

The  building  up  or  the  formation  of  the  three  plant-forms  last 
named  depends  on  the  one  hand  upon  the  mode  of  cell-division,  and 
on  the  other  upon  the  growth  of  the  cells,  individually  and  in  mass. 

A  cell-thread  or  cell-filament  is  a  cell-complex  whose  septa  are 
at  right  angles  to  the  longitudinal  axis,  or  which,  at  least,  presents 
no  longitudinal  septum  when  revolved  upon  its  longitudinal  axis. 
(Numerous  examples  may  be  found  among  the  algae  and  fungi,  as 
well  as  among  various  trichomes  of  higher  plants.) 

45 


46  COMPENDIUM  OF  GENERAL  BOTANY. 

A  cell-surface  is  a  cell-complex  formed  of  a  single  layer  of  cells, 
whose  septa  are  approximately  vertical  to  the  surface  of  the  cell- 
complex,  but  may  form  any  angle  relative  to  each  other.  Ex- 
amples :  some  algae,  moss-leaves. 

A  cell-body  is  a  cell-complex  in  which  the  cells  are  placed  side 
by  side  in  three  directions. 

A  cell-filament  is  formed  from  a  single  cell.  This  may  take 
place  (1)  by  the  exclusive  division  of  an  apical  cell  (Fig.  26  I),  or 
(2)  by  the  combination  of  intercalary  division  with  apical  cell- 
division  (26  II).  In  Fig.  26  II  a  apex  and  base  are  wanting ;  the 
cells  of  the  filament  are  of  nearly  equal  dimensions.  In  Fig.  26 
II  1)  there  is  a  definite  apical  cell  in  which  would  appear  the  fifth 
septum. 

A  cell-surface  may  arise  from  a  single  cell  (Fig.  27  I  a  and  I  b) 
or  from  a  cell-thread  (27  II a  and  lib).  Cell-division  may  be 
wholly  peripheral  in  that  only  the  marginal  cells  divide  (Fig.  27  II I 
represents  an  older  segment  of  a  cell-filament  in  which  this  fact  is 
indicated),  or  the  internal  and  marginal  cells  divide  (27  II  a  and  I  Z>, 
final  stage). 

A  cell-body  may  develop  from  a  cell,  a  cell-filament,  or  a  cell- 
surface.  As  soon  as  cell- walls  in  a  cell  appear  in  three  different 
directions  we  have  a  celt-body.  Here  also  we  may  consider  the 
division  of  inner  and  outer  cells  independently  of  each  other.  We 
shall  proceed  at  once  to  consider  one  of  the  most  important  growth- 
types  of  a  cell-body. 

A.  Stem-structure   among    Vascular    Cryptogams  and  Mosses 
(Fig.  28  «,  £,  c). — Among  Equiselacem  and  many  ferns,  as  well  as 
among  some  leafy  mosses,  there  is  found  at  the  apical  area  of  the 
stem  a  three-sided  pyramidal  (tetrahedral)  cell,  called  the  "apical 
coll."     This  cell  divides,  forming  successive  spirally  arranged  septa. 
Fig.  28  a  presents  a  lateral  view,  28  b  a  surface  view  from  above 
("  apical  view  ").    In  many  instances,  for  example,  in  the  "  bilateral  " 
stem  of  SelagineUa,  the  apical  cell  is  approximately  "  two-edgedo" 
An  apical  view  is  shown  in  Fig.  28  c ;  a  lateral  view  is  similar  to 
Fig.  28  a. 

Since  all  the  cells  of  such  an  organ  can  be  traced  to  the  segments 
of  the  apical  cell,  and  thus  to  the  apical  cell  itself,  we  may  with 
propriety  speak  of  a  single  vegetative  point. 

B.  Root-structure  of  Vascular    Cryptogams  (Fig.   29).  —  The 
tetrahedral  apical  cell  not   only  forms  successive  spiral  segments, 


TISSUES  AND  SIMPLE  ORGANS. 


47 


but  also  cap-segments  for  the  "root-cap"  These  root-cap  segments 
are  the  result  of  partition-walls  formed  parallel  to  the  distal  surface  of 
the  apical  cell,  as  shown  in  Fig.  29.  (In  this  branch  of  anatomy 

Tfi 


n  *- 

3-4     3  — 


£b 


Ih 

2 

1 

2 
2T 

2 

1 

2 

Jh 

2\r 

i 


FIG.  26  I. 


FIG.  26  II  a. 


2J± 
FIG.  26  II  b. 


FIG.  27  I  a. 


FIG.  38  c.  FIG.  29. 

extensive  researches  have  been  made  by  NAGELI,  SCHWENDENEK,  and 
LEITGEB.)     Other  types  of  root-growth  will  be  considered  later. 


48 


COMPENDIUM  OF  GENERAL  BOTANY. 


C.  The  Lichen-Type. — A  collection  of  cell-filaments  form  a  cell- 
body  with  an  apical  cone  similar  to  the  ones  just  mentioned.  The 
filaments  lying  immediately  about  the  axis  in  which  growth  pro- 
ceeds divide  continuously.  Those  lying  some  distance  from  the 
axis  of  growth  seldom  branch.  In  this  form  of  growth  any  given 
point  not  lying  at  the  apex  moves  forward  in  an  "  orthogonal 
trajectory"  until  the  cell-body  has  acquired  its  definitive  width. 

The  following  question  is  important  as  pertaining  to  the  sub- 
ject under  discussion  in  this  chapter. 

How  is  a  tissue  of  similar,  that  is,  of  equally  large,  cells  con- 
verted into  a  tissue  of  unequally  large  cells  ?  Three  methods  will 
be  mentioned  as  being  especially  important :  (1)  inequality  in  the 
length  of  the  cell- wall  formation  of  contiguous  cells  (see  Fig.  30,  A) ; 
(2)  unequal  growth  of  contiguous  cells  (Fig.  31) ;  with  this  condition 
is  very  closely  allied  the  so-called  gliding  growth,  a  phenomenon  of 
which  KRABBE  has  recently  made  a  special  study  ;  (3)  division  in 
cells  of  equal  growth  may  cease  at  different  periods  of  time.  The 
elongated  cells  in  Fig.  30,  B,  are  formed  in  this  manner. 

B 


FIG.  30. 


FIG.  31. 


While  the  formation  of  stems  and  roots  among  mosses  and  in 
the  majority  of  vascular  cryptogams  is  quite  accurately  known  and 
studied,  and  proceeds  approximately  in  the  manner  indicated,  the 
facts  regarding  corresponding  organs  in  phanerogams  are  not  so 
well  known.  Only  in  a  few  cases  was  it  possible  to  demonstrate 
definitely,  or  approximately,  the  presence  of  a  "  single  apical  area." 
For  example,  four  apical  cells  arranged  in  a  quadrant  about  the  axial 
line  were  observed  in  stems  of  Coniferce  (SCHWENDENER).  Other 
observations  (DINGLER,  KORSCHELT)  speak  for  a  single  apical  cell. 
The  difficulty  of  making  the  investigations  explains  the  contradic- 
tory statements.  JOHANNES  HANSTEIN  in  his  time  (about  1868) 
sought  to  demonstrate  the  existence  of  a  special  growth-type  in 
phanerogams.  He  taught  that  there  was  a  special  formative  tissue 
for  the  epidermis,  the  parenchyma,  and  for  the  central  tissue  of 


TISSUES  AND  SIMPLE  ORGANS.  49 

the  root  and  stem.  These  three  formative  tissues  or  histogens  are 
the  dermatogen  (for  the  epidermis),  periblem  (for  the  parenchyma), 
and  plerome  (for  the  central  tissue,  vascular  system).  Though  this 
question  is  still  undecided,  it  is  certain  that  the  sharp  distinction 
between  "  dermatogen,"  "  periblem,"  and  "  plerome  "  cannot  be 
demonstrated  in  many  cases.  According  to  SCHWENDENER  the 
existence  of  the  plerome  as  a  special  histogen  has  not  been  definitely 
proved  in  a  single  instance.1 

B.  DIFFERENTIATION  OF  TISSUES  ACCORDING  TO  STRUCTURE  AND 

FUNCTION. 

(PHYSIOLOGICAL  ANATOMY  OF  SIMPLE  ORGANS.) 
Differences  of  Functions  and  their  Enumeration. 

Although  the  physiological  method  of  investigation  as  applied 
to  the  anatomy  of  plants  (hence  called  the  anatomical-physiological 
tendency)  was  not  unknown  in  the  year  1874,  our  knowledge  con- 
cerning the  relations  of  the  anatomical  structure  to  the  life  of  the 
plant  was  so  imperfect  that  anatomy  in  general  was  almost  entirely 
separated  from  life-processes  and  became  a  matter  of  mere  "  dead  " 
description.  The  question  :  Why  ? — in  other  words  :  Why  are  va- 
rious tissues  and  cell-forms  so  arranged  and  formed  ? — was  made 
applicable  to  the  most  widely  different  internal  organs  of  plants 
after  SCHWENDENER  in  his  work  "  The  Mechanical  Principles  of 
Stem-structure,"  etc.,  had  given  an  important  tissue-system  a  care- 
ful consideration  from  the  teleological  standpoint.  By  it  the  teleo- 
logical  method  of  investigation  received  a  strong  impetus.  These 
preliminary  remarks  are  in  order,  since  in  them  lies  the  justifica- 
tion of  the  arrangement  of  the  greater  part  of  this  book,  especially 
for  the  extensive  discussion  of  tissues. 

We  shall  now  consider  the  important  tissues  according  to  struc- 
ture &nd  function. 

General  considerations  will  show  what  functions  predominate  in 
plant-life  and  why  plant-organs  must  exist. 

The  life  of  the  plant  manifests  itself  in  three  ways.  These 
life-manifestations  are :  nutrition,  growth,  and  reproduction.  A 
series  of  special  functions  are  dependent  upon  these  three  great  life- 
activities. 


1  Sitzungsberichte  der  Berliner  Akad.,  1882. 


50  COMPENDIUM  OF  GENERAL  BOTANT. 

The  process  of  plant  development  is,  as  is  well  known,  not  of 
unlimited  duration.  With  the  formation  of  reproductive  organs 
or  germs  there  is  a  relative  termination  of  active  life,  which  subse- 
quently begins  anew,  so  that  we  speak  of  a  succession  of  generations. 
In  reproduction  (sexual  or  asexual)  a  plant-individual  gives  rise  to  a 
new  individual.  The  mother  individual,  as  a  rule,  is  sooner  or  later 
entirely  destroyed.  Hence  reproduction  serves  to  maintain  the 
species.  Growth  and  nutrition  serve  the  immediate  maintenance 
of  the  plant-individual.  Nutrition  must  of  course  precede  the 
activity  of  growth.  The  inter-relation  of  the  two  is  worthy  of  note. 
We  shall  here  follow  SACHS,  who  has  very  beautifully  demonstrated 
this  fact. 

Growth  can  therefore  only  take  place  as  the  result  of  preceding 
nutrition.  Ordinarily  these  two  processes  take  place  separately 
both  as  to  time  and  place.  "When  seeds  germinate,  when  bulbs  put 
forth  leaves  and  flowers,  when  buds  develop,  they  receive  as  a  rule 
only  water.  Nutrition  for  these  various  growth-processes  has  been 
completed  for  some  time,  usually  by  the  leaves  of  the  preceding  year. 
On  the  other  hand  horse-chestnut  trees,  etc.,  have  stored  within 
themselves  large  quantities  of  food  materials  as  the  result  of  the  work 
of  assimilation  by  the  leaves  during  the  summer  months  while  new 
leaves  and  branches  are  no  longer  formed.  Even  among  annual 
summer  plants,  which,  superficially  considered,  grow  and  nourish 
themselves  at  the  same  time,  a  distinction  in  the  two  processes  can  be 
observed.  In  the  night  there  is  growth  without  nutrition,  during 
day  growth  with  nutrition.  The  work  of  nutrition  is  here  also 
carried  on  by  the  mature  roots  and  leaves,  while  growth  takes  place 
at  various  vegetative  points  or  areas  and  in  the  flowers  and  fruit. 

The  following  is  an  enumeration  of  the  different  special  func- 
tions; most  of  them  belong  to  the  domain  of  nutrition: 

I.  Cell-forming  function  of  formative  tissue. 
II.  Structure  and  function  of  epidermal  tissue-systems. 
III.  Function  of  mechanical  tissues. 

IY.  Function  of  conduction  of  (a)  carbohydrates  and  non-ni- 
trogenous substances,  (b)  of  albuminous  substances,  (<?)  of  water. 

Y.  Protection  of  embryonic  areas  of  the  plant-body. 
YI.  Assimilation  of  carbon. 
YII.  Function  of  aeration. 

YIII.  The  taking  up  of  food  substances  by  means  of  the  roots. 
IX.  The  taking  up  of  assimilated  food-substances. 


TISSUES  AND  SIMPLE  ORGANS.  51 

X.  Storing  of  food-substances. 
XL  Secretion  and  excretion. 
XII.  Reproduction. 

As  a  final  chapter  to  Functions  II,  III,  and  IY  there  will  be 
added  a  discussion  of  the  "  endoderm,"  or  "  protective  sheath." 


SPECIAL   FUNCTIONS. 

I.  THE   FUNCTION  OF  FOEMATIVE   TISSUES   (MERI- 
STEM  AND  CAMBIUM). 

The  process  of  cell-division  during  the  development  of  countless 
plants  and  plant-organs  is  the  principal  cause  of  growth.  Growth  is 
not  equivalent  to  cell-division.  But  in  the  majority  of  the  so-called 
higher  plants  the  function  of  growth  stands  in  close  interrelation  to 
the  function  of  cell-division.  Cell-division  without  growth,  that  is, 
without  increase  in  volume,  is  possible.  It  is,  however,  so  frequently 
associated  with  growth-processes  that  the  considerations  of  the  mo- 
dality of  cell-wall  formation  at  the  same  time  become  considerations 
concerning  growth-types.  This  is  also  proven  by  the  literature 
relating  to  the  earlier  researches  of  NAGELI,  as  well  as  by  the  related 
school  of  evolutionary  development  (KNY,  LEITGEB,  and  others). 

The  following  statements  will  explain  the  relation  of  growth  to 
cell-division. 

With  SACHS  we  distinguish  three  cases. 

1.  Growth  without  Cell-division. — This  rare  occurrence  is  met 
with  in  Siphonacece,  a  group  of  marine  algae.     These  plants  are  very 
large,  but  have  only  a  single  primordial  utricle  with  various  branch- 
ings or  projections  ;  they  have  a  continuous  apical  growth,  while  the 
distal  end  is  closed  by  coagulated  plasm. 

2.  Cell-division  without  Growth. — This  again  is  of  rare  occur- 
rence.    It  is  typically  represented  in  the  algal  group  Sphacelariacece. 
A  single  apical  cell  divides  with  a  transverse  septum.     This  cell, 
which  is  situated  at  the  apical  area  of  the  stem,  represents  the  grow- 
ing part  of  the  plant.     As  soon  as  the  transverse  septum  has  cut 
off  a  posterior  segment  this  segment  ceases  to  grow.     It,  however, 
divides  into  a  large  number  of  cells  by  the  formation  of  numerous 
septa. 


52  COMPENDIUM  OF  GENERAL  BOTANY. 

3.  These  two  rather  rare  extreme  cases  are  opposed  by  the 
great  majority  of  growing  organs,  in  which  development  is  a  com- 
bination of  growth  and  cell-division.  According  to  Sachs,  an  organ 
(example :  stem  or  root)  in  the  process  of  development  may  be 
divided  into  three  regions:  (a)  the  region  of  the  apex  with  active 
cell-division  and  slight  growth  (increase  in  volume),  (b)  the  region 
of  intercalary  elongation  with  enormous  growth  and  moderate  cell- 
division,  (c)  the  region  of  completed  growth. 

According  to  the  heading  of  this  short  chapter,  the  activity  of 
the  vegetative  area,  with  and  without  apical  cell,  would  belong  here. 
Yet  for  reasons  pertaining  to  the  arrangement  of  this  book  this  sub- 
ject has  already  been  touched  upon  in  The  Structure  of  Tissues. 

We  may  designate  the  above-mentioned  vegetative  points  as 
"  embryonic  areas "  with  terminal  position;  while  those  formative 
tissues  whose  function  it  is  to  produce  growth  in  thickness  should 
be  designated  as  "  internal  "  embryonic  areas.  From  the  activity 
of  these  vegetative  areas  result  the  mechanical  and  vascular  tissues, 
and  from  a  practical  standpoint  would  be  treated  in  the  chapter  on 
the  tissues  named.  This  also  applies  to  the  cork-cambinm. 

The  formation  of  secondary  organs  on  pre-existing  organs 
(formation  of  organ-systems)  will  be  more  fully  treated  in  a  subse- 
quent section. 

If,  after  the  mere  mention  of  these  things,  the  reader  should  ask 
why  a  chapter  on  the  cell- forming  function  is  at  all  introduced  at 
this  point,  the  answer  may  be  found  in  the  following : 

A  plant,  whether  it  lives  for  a  period  of  less  than  one  year  or 
over  one  thousand  years,  is  engaged  in  the  formation  of  new  organs 
during  the  annual  vegetative  period  of  its  entire  existence.  These 
developing  organs  must  have  areas  which  are  meristematic  in  char- 
acter. The  most  important  organs  (leaves,  branches,  roots,  fre- 
quently vascular  tissues,  etc.)  are  not  only  formed  once  and  endowed 
with  a  lifelong  function,  but  are  increased  in  number  by  new  similar 
organs,  and  in  the  case  of  loss  are  uniformly  replaced.  Among 
animals  certain  subordinate  organs,  for  example  hairs,  are  endowed 
with  a  lifelong  power  of  regeneration.  However,  constant  neo- 
formation  of  the  most  important  organs  is  not  the  rule,  while  the 
vegetable  organism  is  specially  adapted  in  this  respect.  This 
"function "is  inherently  peculiar.  Its  activity  is  perhaps  not  of 
such  great  importance  to  the  complete  organism  as,  for  example. 
the  activity  of  green  cells  (function  of  assimilation) ;  it  rather 


TISSUES  AND  SIMPLE  ORGANS.  53 

brings  forth  or  awakens  the  activity  of  vegetative  areas  and  ele- 
mentary meristematic  organs  which  through  subsequent  growth 
and  modification  may  subserve  various  functions. 

II.  STRUCTURE  AND  FUNCTION  OF  THE  EPIDEEMAL 
TISSUE-SYSTEM. 

Living  organisms,  in  general,  are  separated  from  their  surround- 
ings by  a  dermis  or  tegumentary  tissue.  The  injurious  influence  of 
its  locnl  or  entire  absence  makes  itself  felt  in  various  ways.  Upon 
examination  we  find  that  the  epidermal  system  of  plants  has  a  three- 
fold significance. 

1.  The  tegumentary  tissue  of  plants,  like  the  skin  of  animals,  has 
a  mechanical  function.     The  more  delicate  parts  of  plants  require  a 
more  resisting  covering  capable  of  protecting  them  against  mechan- 
ical injuries  (pressure,  friction,  etc.). 

2.  The   dermis   of    land-plants    forms    a   necessary  protection 
against  evaporation  in  that  it  is  highly  impermeable  to  water  and 
water-vapor. 

3.  In  land-plants  it  also  forms  a  water-supplying  system.      It 
forms  a  peripheral  enveloping  water-storing  structure  as  opposed  to 
the  internal  water-conducting  tissue  represented  by  the  water-storing 
cells  and  tracheal  system  (vessels,  tracheids). 

These  three  functions  correspond  to  suitable  anatomical  and 
other  adaptations.  In  each  of  the  three  groups  of  adaptations  there 
may  be  noticeable  a  slight  development  or  a  gradual  increase  up  to 
complete  anatomical  conformation,  according  to  requirements. 

Epidermis  may  be  defined  as  a  superficial  cell-covering  of  an 
organ  being  at  least  one  layer  in  thickness.  If  an  increase  in  the 
number  of  these  cell-layers  signifies  an  increase  in  the  mechanical 
or  water-supplying  function,  the  phytotomist  speaks  of  it  as  a 
"  several"-  or  "  many-layered  "  epidermis.  Since  these  layers  under 
certain  conditions  frequently  increase  with  great  regularity,  the  old 
expression  cork-  or  periderm-formatiou  has  been  used  to  designate 
this  change  more  specifically.  Should  this  change  still  proceed  in 
a  manner  to  be  described  later,  it  is  designated  as  bark-formation. 

Before  entering  into  the  anatomical-physiological  treatment  of 
the  threefold  tegumentary  function  it  is  important  to  note  that  in 
the  epidermis  and  vegetable  teguments  in  general  the  cells  are 
closely  united,  not  having  intercellular  spaces.  This  structural  con- 


54 


COMPENDIUM  OF  GENERAL  BOTANY. 


dition  is  found  useful  in  all  of  the  three  forms  of  epidermal 
function.  If  the  contiguous  radial  walls  of  the  epidermis  take  a 
wavy  course  (whereby  their  area  is  also  increased),  it  very  materially 
increases  the  mechanical  resistance  to  the  separation  of  the  contact- 
walls.  In  an  actual  test  rupturing  of  the  tangential  outer  wall 
took  place  much  more  readily  than  separation  of  the  radial  contact- 
walls. 

The  accompanying  figures  show  two  small  portions  of  represent- 
ative epidermal  tissue  in  surface  view. 


FIG.  32. 


FIG.  33, 


In  Fig.  34  are   shown   all  three  epidermal  peculiarities    quite 
well  developed.     Let  us  consider  it  more  in  particular.     The  genus 

Aloe  comprises  plants  adapted  to  with- 
stand  dry  periods ;  therefore  they  have 
?  those  anatomical  features  which  tend 
to  reduce  the  loss  of  moisture  well 
developed.  The  cuticle  inclusive  of 
the  cuticular  layers  (cs  =  cuticular 
layers,  c  =  cuticle,  b  =  cellulose)  is 
very  thick.  The  cuticula  is  a  thin 
membrane  highly  impermeable  to 

-Epidermal  cells  of  the  water>  jt  re8Ulted  from  fatty  and 
waxy  deposits  in  the  cellulose-mem- 
brane (cuticularization).  In  many  of  our  indigenous  plants  this 
cuticula  is  exceedingly  thin,  but  is  present  in  all  plants;  in  sub- 
merged water-plants  it  is  almost  reduced  to  zero  (No.  2). 

The  thickness  of  the  entire  outer  wall  inclusive  of  the  thickened 


FIG.  34. 

leaf  of  Aloe  acinacifolia. 
(After  Haberlandt.) 


TISSUES  AND  SIMPLE  ORGANS.  55 

outer  portions  of  the  radial  walls  furnishes  the  mechanical  support. 
In  the  indigenous  foliage  leaves  which  live  only  a  few  months  this 
character  is  correspondingly  reduced  (No.  1). 

As  a  rule,  the  greater  portion  of  the  epidermal  cell-contents 
is  water  (No.  3,  p.  53).  Eed  and  other  coloring  materials  are 
frequently  found  in  solution.  The  absence  of  chlorophyll  is  a  very 
prominent  anatomical  characteristic  of  epidermal  water-supplying 
tissues.  "We  have  now  touched  lightly  upon  the  three  functions 
mentioned. 

In  water-plants  chlorophyll  is  very  plentiful  in  the  epidermal 
cell-layer.  This  does  not  at  all  signify  that  a  "  tegument "  or 
"epidermis'7  is  wanting.  An  epidermal  water-storing  tissue  is, 
however,  wanting,  while  we  find  well-marked  evidence  of  epidermal 
characteristics  which  find  expression  in  a  considerable  thickness  of 
the  outer  wall,  that  is,  mechanical  characteristics,  since  that  alone 
is  found  to  be  useful.  For  example,  in  case  of  injuries  water  would 
enter  the  air  chambers  in  the  interior  and  expel  the  much-needed 
air  (see  Aeration). 

We  speak  of  increase  in  the  functional  activity  of  epidermal 
systems.  As  a  rule,  the  amount  of  water  in  the  epidermal  water- 
tissue  increases  with  the  depth  of  the  single-layer  epidermis  and 
with  the  number  of  layers  in  the  many-layered  epidermis.  Most 
of  our  indigenous  plants  have  an  epidermis  of  a  single  layer,  with 
various  gradations  in  the  thickness  of  this  single  layer.  Leaves 
which  are  exposed  to  considerable  dry  ness  (Ficus,  etc.)  have  several 
layers. 

As  a  result  of  excessive  loss  of  water  the  thinness  of  the  radial 
walls  (Fig.  34)  permits  not  only  of  shortening,  but  of  wavy  foldings. 
The  latter,  according  to  our  conception,  is  for  the  special  protection 
of  green  tissues.  It  can  be  clearly  shown  that  epidermal  and 
internal  water-tissue  cells  are  the  first  to  suffer  from  loss  of  water. 
The  assimilating  cells  may  endure  a  much  longer  time  without 
visible  signs  of  material  loss. 

Certain  leaves  of  Bromeliaceae  show  epidermal  structures  of 
several  layers  thickness  in  the  part  functioning  mechanically  as  well 
as  in  the  part  functioning  as  a  water-reservoir.  Thin  radial  walls 
are  not  always  present.  For  example,  in  the  epidermal  structures  of 
xerophilous  plants  (desert  plants,  plants  accustomed  to  excessive 
dryness)  we  find  thick  radial  walls ;  these  have,  however,  numerous 
pores  which  facilitate  the  exchange  of  water  in  the  water-tiseue. 


56  COMPENDIUM  OF  GENERAL  BOTANY. 

The  thin  walls  have,  so  to  speak,  become  sacrificed  to  the  first  two 
functions  (p.  53). 

This  explains  the  water-storing  and  the  mechanical  function  of 
the  tegumentary  system.  We  must  now  discuss  somewhat  more  in 
detail  the  function  of  "  protection  against  evaporation."  For  a  long 
time  we  have  made  a  practical  and  technical  use  of  the  peculiar 
properties  of  corky  or  cuticularized  membranes.  They  are  used 
in  a  similar  manner  as  by  plants.  Cork  serves  to  close  vessels  con- 
taining liquids,  to  prevent  leakage.  Sometimes  sealing-wax,  resin, 
or  some  other  waxlike  substance  is  added  to  prevent  excessive  loss 
by  evaporation.  So  we  find  waxy  excretions  and  waxy  coatings  on 
plants  of  those  climates  with  periods  of  dryness.  YOLKENS*  reports 
a  desert-plant  whose  leaves  are  coated  with  a  resinous  substance. 
This  structural  change  corresponds  with  a  functional  increase  of  the 
cuticula. 

We  now  come  to  the  consideration  of  cork  and  bark.  These 
formations,  though  they  may  form  layers  several  inches  in  thickness, 
are  nevertheless  physiologically  related  to  the  cuticle,  which  is 
frequently  immeasurably  thin. 

Cork  and  Bark. — While,  as  above  stated,  the  epidermis  consists 
of  a  single  layer  of  cells,  the  bark-covering,  as  a  rule,  consists  of 
several  or  many  layers  of  cells.  Cork  several  layers  in  thickness 
may  result  from  simple  cnticularization  of  ordinary  parenchyma- 
cells,  but  in  the  majority  of  cases  cork  is  the  result  of  a  special 
process  of  cell-division.  This  process  of  cell-division  has  the 
greatest  similarity  to  "  cambial  activity,"  that  is,  to  the  cell-form- 
ing process  in  the  ring  between  the  wood  and  bark  (cambium -ring) 
of  our  trees. 

In  the  case  first  mentioned  the  cork-cells  do  not  necessarily  lie 
in  radial  series,  while  in  the  latter  case  this  arrangement  is  charac- 
teristic. The  cork-cambium  (phellogen),  as  well  as  the  above- 
mentioned  cambium  between  wood  and  bark,  is,  as  a  rule,  a  bipolar 
formative  tissue.  In  only  a  few  cases  it  is  one-sided,  that  is,  forms 
cells  which  become  cuticularized  from  without  inward.  Ordinarily 
in  bipolar  cork-cambium  activity  the  numerous  outer  cells  become 
cuticularized  centripetally.  There  are  formed  inwardly  less  numer- 


1  The  same  investigator  observed  a  shrub  (Reaumuria  Mrtella)  in  the  Arabian 
desert  in  which  epidermal  glands  secrete  a  hygroscopic  saline  substance  which 
absorbs  moisture  from  the  air  during  the  night. 


TISSUES  AND  SIMPLE  ORGANS. 


57 


ous  cells  of  the  character  of  primary  parenchyma  called  "  phel- 
loderm,"  or  "  cork-parenchyma  cells."  The  various  layers  formed 
outwardly  are  not  all  equal  :  there  may  be  alternate  layers  with 
thick  and  thin  cell-walls  (Betula  alba). 

The  well-known  "  peeling"  or  "scaling"  of  bark  will  occur 
very  readily  along  the  thin-walled  layers,  because  they  are  only 
slightly  extensible  as  compared  with  the  thick-walled  layers,  in 
which  cellulose  predominates.  The  thin-walled  layers  consist 
essentially  of  suberin,  a  fatty  substance,  which,  besides  other  con- 
stituents, contains  stearin  (v.  HOHNEL,  KUGLER).  The  microscopist 
recognizes  cuticularized  membranes  by  their  insolubility  in  con- 
centrated sulphuric  acid.  According  to  AMBEONN,  fat-crystals  may 
readily  be  detected  in  the  cuticle  (cuticula)  by  means  of  polarized 
light. 


FIG.  35. — Transverse  section  of  Ribes  nigrum  from  a  twig  one  year  old. 

e,  Epidermis;  h,  hair-cell;  »r,  bark -parenchyma;  K,  product  of  the  cork-cambium  c;  fc,  cork- 
cells;  pd,  chlorophyll-bearing  cells;  6,  bast-cells.    (After  Sachs.) 

When  and  where  is  cork-formation  necessary?  Harmonizing 
with  the  properties  of  cuticularized  cells-walls,  a  corky  protective 
tissue  is  required  on  the  following  plant-structures :  at  points 
where  the  cuticle  and  epidermis  are  ruptured  because  of  the  growth 
in  thickness  of  the  stem  or  root ;  on  delicate  plant-structures  which 


58  COMPENDIUM  OF  GENERAL  BOTANY. 

are  habitutally  or  accidentally  exposed  ;  on  the  leaf-scars ;  on 
injured  plant-tissues;  on  subterranean  organs  which  must  be  pro- 
tected against  excessive  moisture  (for  example,  potato-tubers,  older 
roots  and  rootlets1).  In  the  chapter  on  Reproduction  the  cuticu- 
larization  of  the  outer  coverings  of  pollen-grains  and  spores 
will  be  discussed.  This  secondary  corky  change  has  a  bearing  on 
the  ability  to  resist  atmospheric  changes  for  a  shorter  or  longer 
time  (resting  period). 

In  all  these  cases  a  protective  tissue  is  required.  Usually  this 
tissue  has  the  power  of  continuous  regeneration.  We  find  corky 
tissues  in  older  roots,  in  subterranean  stems,  on  leaf-scars,  and,  most 
common  of  all,  as  a  covering  of  the  cambium-ring  of  growing  tree- 
stems.  Each  of  these  cases  we  must  discuss  more  in  detail. 

Scar-tissue  ( Wundkork). — The  prick  of  a  needle  into  a  develop- 
ing potato-tuber,  or  into  the  young  stem  of  a  woody  plant,  causes 
the  death  of  the  injured  cells,  and  perhaps  of  a  few  others  in  their 
immediate  vicinity.  In  nature  such  injuries  may  result  from 
stings  or  bites  of  various  animals.  The  uninjured  cells  surrounding 
the  injured  part  at  once  proceed  to  divide  parallel  to  the  injured 
surface,  that  is,  tangential  to  the  centrally  located  injured  cells.  For 
example,  an  injury  resulting  from  the  puncture  made  by  a  needle  will 
develop  a  cylindrical  covering  of  suberized  cells.  This  scar-tissue 
separates  the  injured  (in  other  cases  diseased)  portion  from  the  normal 
tissue,  and  at  the  same  time  prevents  the  evaporation  of  moisture 
from  the  injured  surface. 

Falling  of  Leaves. — Before  the  leaves  begin  to  fall  in  the  autumn 
a  "  scission-layer  "  is  formed  between  the  base  of  the  petiole  and 
the  stem.  A  separation  of  the  cells  of  this  layer  causes  the  leaves 
to  fall  off.  In  a  large  number  of  instances  the  formation  within 
the  scission-layer  of  a  plate  of  ice  which  subsequently  melts,2 
causes  the  profuse  falling  of  leaves  noticeable  in  the  fall.  The 
scission-layer  is,  however,  not  the  protective  covering.  A  pro- 
visional protection  is  formed  by  a  mucilaginous  substance  known  as 
callus,  which  closes  the  vessels  ;  or  by  the  '•  tyloses,"  that  is,  certain 
cellular  protrusions  which  grow  into  the  vascular  system  from  the 
cells  of  its  immediate  surroundings.  Drying  forms  a  provisional 
protection  for  the  parenchyma  (perhaps  in  connection  with  a  chem- 


1  Also  on  the  root-tubercles  of  Leguminosw  and  Cycas  revoluta. — TRANS. 

2  MOHL,  Botanische  Zeitung,  1860,  and  Sachs,  Vorlesungen. 


TISSUES  AND  SIMPLE  ORGANS.  5& 

ical  metamorphosis  which  is  not  well  understood).  The  final  pro- 
tection, however,  is  afforded  by  the  formation  of  a  layer  of  cork, 
which  in  some  cases  begins  to  develop  some  time  before  the  falling 
of  the  leaf  ;  in  other  cases  it  begins  later,  and  permanently  supplants 
the  provisional  protection. 

The  above-mentioned  phenomena  offered  great  difficulties  to 
NAGELI,  who  in  his  theory  of  natural  descent  asserts  that  a  stimulus 
gives  rise  to  an  organ.  We  ask :  1.  What  stimulus  calls  forth  the 
formation  of  a  scission-layer?  2.  What  stimulus  gives  rise  to  the 
beginnings  of  scar-tissue  formation,  even  some  time  before  a  scar  is 
present  ?  To  return  to  our  subject,  I  will  state  for  the  benefit  of 
those  who  wish  to  enter  more  deeply  into  these  relations  that  the 
vascular  system  of  leaves  ("  leaf  -trace")  of  many  growing  trees  is 
abscised  three  times,  or  even  oftener,  in  the  course  of  the  vegetative 
period  ;  first  by  the  falling  of  the  leaf,  then  again  a  little  below  the 
leaf-scar  by  the  above-mentioned  scar-tissue  formation,  and  finally 
still  deeper  in  the  interior  of  the  cambium  by  the  growth  in  thick- 
ness of  the  stem  (this  occurs  repeatedly  among  evergreen  conifers). 

The  necessity  for  the  cork-tissue  formation  on  stems  growing  in 
thickness  has  already  been  indicated.  In  only  a  few  instances  can 
the  growth  of  the  cuticularized  epidermis  keep  pace  with  the  growth 
in  thickness  of  the  stem  ;  as  a  result  it  is  ruptured.  From  this 
follows  the  necessity  of  a  new,  somewhat  more  deeply  located,  layer 
of  cork  to  guard  against  excessive  evaporation.  The  plant  behaves,, 
if  the  expression  may  be  allowed,  as  if  it  knew  what  would  happen 
later.  Such  " knowing"  is,  however,  excluded:  the  occurrence  of 
suitable  processes  is  only  in  obedience  to  natural  laws  given  by  the 
Creator.  Human  intelligence  is  capable  of  comprehending  the 
teleological  moment  of  these  and  similar  adaptations.  The  causal- 
mechanics,  the  causa  efficiens,  of  the  development  of  cork-tissue  is, 
however,  unknown  to  us  ;  this  is  usually  the  case. 

Since  the  cambium-ring  continues  its  activity  for  years,  the 
cork-covering  first  formed  shares  the  destiny  of  the  epidermis ;  it 
is  ruptured,  and  again  a  substitute  is  formed  in  the  interior : 
that  is,  other  cells  situated  more  and  more  toward  the  interior 
become  suberized. 

One  of  the  most  useful  exercises  for  the  beginner  in  plant- 
anatomy  is  to  find  the  exact  location  of  the  first  cork-formation  in 
stems  and  roots.  Such  investigations  teach  that  in  the  stems  the 
epidermis  itself  may  give  rise  to  cork-formation  (ph  in  Fig.  36 


COMPENDIUM  OF  GENERAL  BOTANY. 


B  =  cork-cambium).  Usual! j  it  begins  in  a  more  deeply  located 
layer  of  the  parenchyma  (Fig.  85).  In  roots  the  seat  of  cork- 
formation  is,  as  a  rule,  found  in  the  peri- 
cambium.  Concerning  this  pericambium, 
we  will  at  this  point  state  only  that  it  is 
a  tissue  one  or  more  layers  in  thickness, 
lying  within  the  primary  root-parenchyma 
outside  of  the  centrally  located  vascular 
bundle. 

Cork  is  a  complex  structure,  com- 
posed of  different  elements,  but  its  origin 
can  be  easily  determined.  As  a  rule,  it  is 
developed  according  to  a  twofold  plan- 
either  as  ring-cork,  or  as  scaly  cork. 
From  the  nature  of  things  tissues  which 
are  separated  from  the  sap-bearing  tissue 

FIG.  36.-Tw"  stages  of  cork-  of  the  interior  by  a  corky  layer  are  subject 
formation  in  the  stem  of  Scu-  to  desiccation.  It  is  also  a  rule  that  one  and 
tellaria  splendens.  ,  ,  .  -/ 

(After  Haberiandt.)  the  same  cork-cambium  does  not  possess 

an   unlimited  power  of  growth,  as  is  the 

case  in  the  cambium-ring  of  our  trees.  The  cork-cambium  discon- 
tinues its  cell-forming  activity,  while  a  new  zone  of  cork-cambium 
appears  more  in  the  interior  ;  this  new  layer  bears  the  same  relation 
to  others,  etc.  Either  these  successive  cork-layers  have  the  form 
of  continuous  cylinders, — in  which  case  they  appear  as  rings  in 
cross-section,  and  the  bark  peels  off  in  cylindrical  pieces, — or  the 
successively  formed  cork-cambiums  (and  their  products)  have  the 
form  of  watch-crystals  or  similar  curved  surfaces  whose  convexities 
are  directed  inward,  appearing  as  partial  circles  in  cross-section,  and 
in  some  cases  (Platanus,  for  example)  forming  scales  whixjh  peel  off 
very  perfectly,  leaving  the  stem  quite  smooth;  in  other  cases  the 
scales  remain  attached  in  large  numbers  for  some  time,  the  bark 
becomes  very  rough  with  deep  crevices,  and  the  scales  are  thrown 
off  at  irregular  intervals.  Hence  "bark"  at  first  contains  the 
elements  of  the  primary  parenchyma  between  its  cork-lamellae,  later 
also  those  of  the  secondary  parenchyma,  still  later  only  those  of  the 
secondary  parenchyma. 

Besides  the  above-mentioned  conditions  in  the  case  of  birch-bark 
(Betula\  thin-walled  and  thick- walled  unsulerized  cells,  which  are 
intercalated  between  the  suberized  cells,  are  sometimes  formed  in 


TISSUES  AND  SIMPLE  ORGANS.  61 

other  plants.  These  are  the  so-called  "  scissiou-phelloids "  of  v. 
HOHNEL/  which  have  the  function  of  bringing  about  the  scaling  of 
the  bark. 

The  scar-cork  or  scar-tissue  has  been  mentioned  above.  When 
the  living  cells  of  various  tissues  are  injured  or  killed,  the  neigh- 
boring cells  are  sometimes  enabled  to  create  a  protective  covering  at 
once,  having  therefore  the  behavior  of  cork-cambium.  It  is  not 
within  the  province  of  this  book  to  enter  into  a  discussion  of  prac- 
tical arboriculture.  I  cannot,  however,  omit  pointing  out  the  funda- 
mental principles  underlying  all  those  operations  which  are  of  such 
importance  in  fruit-tree  culture,  namely  grafting.  In  the  various 
kinds  of  grafting,  such  as  root-grafting,  side-grafting,  saddle-graft- 
ing, bud-grafting,  etc.,  injuries  must  of  necessity  occur ;  while  in  all 
cases  an  effort  is  made  to  induce  the  separated  parts  to  grow 
together.  One  essential  to  bring  about  such  a  union  is  that  cam- 
bium must  be  in  contact  with  cambium.  The  growing  together  of 
separated  tissues  sometimes  takes  place  during  the  natural  develop- 
ment of  plants ;  but  caution  is  necessary  in  the  explanation  of  such 
phenomena  in  order  to  avoid  the  mistake  of  pronouncing  tissues  as 
having  grown  together  which  were  in  reality  never  separated. 
The  phanerogamic  parasites  form  a  growth-union  with  the  host 
plants,  while  the  basal  parts  of  sympetalous  (united  petals)  corollas 
have  never  been  separate. 

Structural  Aids  to  the  Function  of  Cork-tissue  and  Cuticula 
(cuticle). —  Trichomatic  Organs  (trichomes). — In  harmony  with  the 
subject  under  discussion  the  question  might  arise,  Are  there  still 
other  structures,  besides  the  epidermal  system  with  its  cuticular  and 
cork-forrnations,  which  serve  to  protect  plants  against  excessive 
drying  ?  As  is  to  be  expected,  this  question  is  answered  in  the 
affirmative.  Among  other  works,  the  reader  interested  in  this  sub- 
ject will  find  valuable  information  in  YOLKENS'  "  Flora  of  the 
Arabian  Desert "  (Berlin,  1887).  I  will  touch  briefly  upon  the 
salient  details. 

The  limitation  of  the  entire  life  of  desert  plants  to  the  most 
suitable  period  of  the  year  (period  of  rainfall),  therefore  also  the 
hastening  of  the  vegetative  period,  then  the  transfer  of  the  time  of 


1  Wiener  akad.  Sitzungsber.,  LXXVI,  1.  Abtheilung.  J.  E.  Weiss  has  also 
written  on  the  same  subject  (Deukschrift.  d.  K.  Bot.  Ges.  zu  Regeusburg,  1890, 
VI). 


62  COMPENDIUM  OF  GENERAL  BOTANY. 

vegetation  to  the  most  suitable  period  of  the  year,  will  first  be  con- 
sidered. The  formation  of  roots  reaching  deep  into  the  soil,  the 
surrounding  of  the  roots  with  sand  and  particles  of  earth  by  means 
of  the  root-hairs,  which  usually  serve  to  take  up  food  materials,  the 
hygroscopic  salts  mentioned  on  page  56,  the  retention  of  rain  and 


A,  Climbing  hair-cell  of  Humulus. 


FIG.  37. 

7?,  Climbing  hair-cell  of  Phaseolus.     C,  Adjacent  margins 


of  two  pappus-scales  of  Galinsfga  parviflora.  Ca,  hair-cell  of  Urtica  urens ;  Cb,  upper 
end  of  the  same  ;  Cc,  the  same  with  tip  removed  at  z.  D,  Scaly  compound  hair-cell  from 
the  leaf  of  Hippophae  rhamnoides.  E,  Twining  hair-cell  of  the  calyptra  of  Polytrichum 
juniperinum.  (After  Haberlandt.) 

dew  by  means  of  the  trichomes,  must  all  be  considered  as  means  to 
the  end  under  consideration.  Along  with  these  structural  arrange- 
ments— especially  the  arrangement  for  the  taking  up  of  water — there 
are  also  adjustments  for  retarding  the  loss  of  moisture,  such  as  the 
reduction  of  the  evaporating  surfaces ;  the  leaf-formation  may  be 


TISSUES  AND  SIMPLE  ORGANS.  63 

absent  or  reduced  to  a  minimum,  in  which  case  the  stem-parenchyrna 
alone  carries  on  the  process  of  assimilation ;  other  means  are  the 
rolling  up,  curling,  or  folding  of  the  leaf -surf  aces,  the  vertical 
position  of  leaf-blades,  and  the  formation  of  mucilaginous  substances 
in  the  epidermis  for  the  purpose  of  retaining  moisture.  Later,  in 
the  discussion  of  the  aerating  system,  we  will  learn  to  know  another 
characteristic  phenomenon  occurring  in  various  forms  which  has  to 
do  with  the  position  and  structure  of  stomata  (the  openings  of  the 
aerating  system).  This  phenomenon  also  belongs  to  the  above- 
enumerated  arrangements  for  reducing  the  loss  of  moisture. 

The  mention  of  trichomes  made  above  lead  me  to  make  the 
following  statement.  The  anatomy  of  trichomatic  organs  has  been 
accurately  studied  ;  their  physiological  significance  is,  however,  not 
correspondingly  well  known.  For  that  reason  I  shall  conclude  this 
chapter  rather  hurriedly.  Of  the  great  variety  of  forms  of  trichomes 
I  shall  select  only  a  few  represented  in  Fig.  37.  If  a  glandular  hair 
secretes  an  ethereal  oil,  its  function  seems  clear,  namely,  to  attract 
insects  which  will  carry  the  pollen.  If  the  secretion  is  of  a  sticky 
consistency  it  evidently  serves  to  keep  off  injurious  crawling  in- 
sects, since  these  take  the  honey  without  aiding  in  cross-fertiliza- 
tion. The  flattened  or  shield  like  trichomes  which  cover  the  breath- 
ing-pores evidently  serve  to  guard  against  excessive  loss  of  moisture. 
The  satinlike  shimmer  of  floral  leaves  is  due  to  papillose  trichomes 
(conical  projecting  epidermal  cells).  In  some  instances  it  has  been 
proven  that  trichomes  with  thin- walled  areas  near  the  base  serve  to 
admit  moisture  (rain,  dew).  Still  a  considerable  number  of  trichorne- 
structures  remain  whose  physiological  significance  is  not  satisfac- 
torily explained. 

III.  FUNCTION  OF  MECHANICAL  TISSUES. 

Even  a  superficial  consideration  of  the  plant  kingdom  suffices  to 
teach  that  the  mechanical  influences  surrounding  land-plants,  water- 
plants,  aerial  organs,  subterranean  organs,  etc.,  are  different,  and 
that  these  various  plants  and  plant-organs  require  definite  adaptations 
as  to  the  firmness  of  the  tissues  concerned  in  order  that  they  (as  the 
normal  course  of  things  teaches)  may  be  maintained  in  their  entirety. 

In  upright  stems — in  fact,  in  all  organs  which  must  maintain 
themselves  in  an  upright  or  in  a  free  horizontal  position — bending 
enters  into  consideration,  especially  as  the  result  of  air  currents;  also 


64  COMPENDIUM  OF  GENERAL  BOTANY. 

of  the  weight  of  the  leaves  and  stems,  of  the  snow,  ice,  etc.  The 
roots  of  a  tree  through  whose  crown  the  wind  blows,  and  the  grass- 
stem  the  panicle  of  which  offers  resistance  to  air  currents,  are  subject 
to  &  pulling  tension.  The  margins  of  flat  leaves  waving  in  the  wind 
are  subject  to  tearing  and  breaking.  Parts  of  winding  stems 
wound  about  dead  supports,  and  more  especially  those  wound  about 
living  supports  (tree-stems  growing  in  thickness),  and  tendrils 
must  resist  pulling  tensions;  likewise  water-plants  in  rapidly  flow- 
ing water,  and  stems  of  hanging  fruit.  Rarely  there  comes  into 
play  a  supporting  tension  similar  to  that  of  a  pillar,  as  in  the  case  of 
supporting  roots.1 

The  question  now  is,  How  are  such  mechanical  requirements  to 
be  interpreted  ?  One  difficulty  will  be  to  explain  these  interesting 
relations  briefly,  yet  not  at  the  expense  of  clearness.  In  many 
respects  the  brief  suggestions  given  in  these  lines,  in  other  cases  a 
hasty  outlining,  will  assist  in  finding  the  necessary  explanations. 

While  I  shall  attempt  to  demonstrate  the  mechanical  principles 
in  the  internal  structure  of  plants  by  giving  a  few  examples,  I  shall 
base  my  discussion  of  the  subject  upon  SCHWENDENER'S  "  Mechanical 
Principles,  etc.,"  as  well  as  upon  NAGELI  and  SCHWENDENER'S 
"  Microscope." 

As  has  been  demonstrated  (SCHWENDENER),  there  is  in  the 
vegetable  kingdom  a  specific  mechanical  tissue- system,  consisting  of 
specific  mechanical  cells,  which  in  its  best  quality  has  the  same  sup- 
porting power  as  malleable  iron  wire,  namely,  twenty  kilos  per 
square  millimeter  (within  the  limit  of  elasticity}.  These  mechanical 
cells  are  designated  by  different  authors  as  :  stereids,  skeleton-cells, 
mechanical  cells,  thick-walled  bast,  hard  bast,  prosenchyma-fibres, 
bast-cells,  sclerenchyma-fibres.3  In  organs  subject  to  bending  the 
mechanical  cells  are  peripherally  located,  while  in  organs  subject  to 
a  pulling  tension  they  are  centrally  located  ;  that  is,  in  typical 
cases  they  are  arranged  according  to  rational  mechanical  prin- 
ciples. That  such  an  arrangement  of  mechanical  cells  is  a  rational 
one  is  made  clear  by  the  following  elementary  considerations  (com- 
pare the  accompanying  figures,  38-42,  as  well  as  those  pertaining 
to  the  root  anatomy). 


1  Aerial  roots  of  Zea  Mays  afford  a  typical  example.     It  does  not  seem  clear 
why  all  vertical  tissues  are  not  subject  to  such  a  tension. — TRANS. 

2  No  doubt  we  must  wait  some  time  before  a  uniform  terminology  will  be 
adopted. 


TISSUES  AND  SIMPLE  ORGANS.  65 

T.  The  fibres  and  tissue-layers  of  a  beam  supported  at  both  ends 
having  a  weight  in  the  middle  are  so  influenced  that  the  uppermost 
fibres  are  most  strongly  pressed  together  and  the  lowermost  fibres 
are  pulled.  In  the  middle  of  the  beam  in  cross-section  there  is  an 
imaginary  "  neutral"  fibre  in  which  the  pressing  tension  passes  into 
a  pulling  tension.  In  this  region  pushing  and  pulling  are  at  a 
minimum.  From  this  it  follows  that  in  order  to  have  an  appropriate 
distribution  of  material  in  such  a  beam  it  must,  in  general,  have  the 
form  (in  cross-section)  of  two  capital  T's,  one  of  which  is  inverted, 
thus  (S3),  since  the  mass  of  material  must  be  distributed  at  the 
points  of  greatest  tension.  In  following  out  this  idea  one  can 
readily  understand  that  a  hollow  cylinder  would  represent  a  type  of 
structure  adapted  to  resist  a  bending  tension  from  all  sides.  The 
combination  of  many  double-T  supports  will  give  us  a  polygon 
whose  sides  are  represented  by  the  cross-lines  of  the  T's.  These 
'  cross-lines,  as  already  stated,  indicate  the  strongest  parts  of  the  sup- 
port ("  girth  ") ;  the  radial  connecting  lines  ("  filling  ")  may  be 
much  weaker;  when  the  "  girth"  becomes  continuous,  the  "  filling" 
may  be  entirely  omitted. 

II.  In  the  determination  of  the  equilibrium  of  a  prismatic  staff 
bent  to  one  side  by  some  lateral  force  we  must  first  of  all  find  the 
"modulus  of  elasticity."     This  maybe  found  as  follows  (it  must 
be  remembered  that  in  the  rational  construction  of  this  formula  no 
fibre  is  to  be  stretched  or  elongated  beyond  the  limit  of  elasticity) : 
If  we  let  A  represent  the  area,  in  cross-section,  of  the  tissue  to  be 
tested,    W  the  maximun  weight  which  can  be  supported  without 
permanent  elongation,  then  the  supporting  power  within  the  limit 

W 

of  elasticity  per  unit  of  surface   U=  -j.     By  dividing   U  by  the 

specific  elongation  due  to  W,  that  is,  y,  in  which  A  equals  the  elonga- 
tion due  to  the  tension  and  I  the  original  length,  the  modulus  of 
elasticity  is  found  E  =  U.  -i-.1 

A 

III.  Besides   the  modulus  of  elasticity,  there  is   still   another 
factor  which  enters  into  the  determination  of  the  equilibrium  of  a 
bent  twig  or  staff. 


1  In  normal  well-developed  bast  1000  units  (in  length)  of  I  equal  about  13  units 
of  A,  U  =  20,  hence  E=  1540. 


66 


COMPENDIUM  OF  GENERAL  BOTANY. 


FIG.  39. — Cross-section  of  the  stem  of  Scirpus  ccespitosiis. 
(After  Haberlandt.) 


B 


FIG.  38.— Mechanical 
cells    in    cross    (B) 
and  longitudinal 
section  (A). 
(After  Haberlandt.) 


FIG.  40.— Bast-ring  of  the  stem  of  Molinia  ccerulea. 
(After  Haberlandt.) 


FIG.  41.— Mid-rib  of  the  leaf  of  Zea 


(After  Haberlandt.) 


FIG.  42. — Transverse  section  of  the 

rhizome  of  Carex  glauca. 

(After  Haberlandt.) 


TISSUES  AND  SIMPLE  ORGANS.  67 

Let  us  make  a  simple  experiment  with  a  ruler.  With  one  of  its 
flat  sides  turned  upward  it  may  readily  be  broken  by  a  force  acting 
downward  or  upward.  If  the  same  force  acting  in  the  same  direc- 
tion acts  upon  the  ruler  with  one  of  its  edges  turned  upward,  then 
it  will  scarcely  be  perceptibly  bent.  In  the  latter  case  forces  in- 
herent in  the  woody  fibres  are  brought  into  play  to  counteract  or 
equilibrate  the  bending  force;  in  the  former  case  this  does  not 
occur.  From  this  it  is  evident  that  in  order  to  determine  the  point 
of  equilibrium  there  is  besides  E  another  magnitude,  the  so-called 
moment  of  flexibility  (Biegungsmoment).  The  latter  ( W)  is 
dependent  upon  the  form  and  area  of  the  transverse  section.  In 
the  case  of  the  ruler  it  is  evidently  the  form  of  the  cross-section, 
which  differs  in  the  two  positions.  TFis  found  by  multiplying  the 
area  of  each  element  in  cross-section  by  the  square  of  its  distance 
from  the  neutral  point,  and  then  adding  the  number  of  such  prod- 
ucts in  the  entire  cross-section.1  (The  limit  or  amount  of  flexibil- 
ity to  be  determined  experimentally  depends  essentially  upon  W 
and  E.} 

From  the  above  illustration  with  the  ruler  it  follows  that  the 
pressing  and  pulling  forces  (of  opposite  elements)  resulting  from  a 
lateral  pressure  upon  a  beam  is  inversely  proportional  to  the  distance 
of  the  girdings.  The  supporting  power  of  the  beam  increases  not 
only  with  the  strength  of  the  girdings,  but  also  with  their  relative 
distance  of  separation  ;  that  is,  the  stronger  the  girdings  the  farther 
they  may  be  apart  in  order  to  give  a  maximum  effect. 

This  principle  of  the  peripheral  arrangement  of  firm  elements 
in  supporting  organs,  though  simple,  is  most  extensively  embodied 
in  multitudinous  forms  in  the  arrangement  of  mechanical  plant- 
cells.  As  it  is  customary  in  technics  when  using  two  different  ma- 
terials— for  example,  wood  and  iron — to  place  the  stronger  material 
where  the  greatest  support  is  to  be  maintained,  that  is,  at  the  girding, 
while  the  weaker  material  is  used  as  filling,  so  it  is  found  that 
mechanical  cells  in  the  supporting  tissues  of  plant-organs  are  pe- 
ripherally arranged,  while  other  tissues  which  serve  the  purpose  of 
nutrition,  storing  of  food  material,  conduction  of  fluids,  etc.,  repre- 
sent the  filling  material.  It  is  to  be  expected  that  the  assimilating 
system,  dependent  upon  sunlight  for  its  activity  (chlorophyll-bear- 


1  Let  A  equal  the  area  in  cross-section  of  one  element,  r  its  distance  from  the 
neutral  point;  then  A.  r*  =  the  moment  of  flexibility  of  a  given  element. — TRANS. 


68  COMPENDIUM  OF  GENERAL  BOTANY. 

ing  tissues),  and  which  is  also  peripherally  located,  must  make 
suitable  concessions  to  the  mechanical  tissues  as  to  position.  This 
is  what  actually  takes  place. 

IY.  Theoretically  the  strength  of  a  given  support  would  depend 
only  upon  the  magnitude  of  its  cross-section.  It  is,  however,  evi- 
dent that  six  silk  threads  which  are  about  one  cm.  apart  and  so 
placed  that  one  is  central  and  the  other  five  peripheral,  are  in  danger 
of  being  torn  by  some  pulling  force,  because  tension  on  them  is 
very  apt  to  be  unequal.  This  unequal  tension  may  be  counter- 
acted to  a  considerable  degree  by  bringing  the  threads  in  contact  so 
that  tension  will  act  on  all  of  them  at  the  same  time.  The  consid- 
eration of  various  roots  which  are  also  subject  to  pulling  tensions 
teaches  that  a  central  arrangement  of  mechanically  resisting  elements 
is  the  intended  plan  of  structure.  According  to  a  similar  principle, 
the  centripetal  tendency  of  mechanical  elements  is  also  found  in 
such  structures  as  tendrils,  plant-organs  in  rapidly  flowing  water, 
stems  of  climbing  plants,  and  stalks  of  fruits.  In  rhizomes,  which 
morphology  shows  to  be  stems,  and  in  running  stems  (creepers), 
the  anatomist  finds  a  tendency  on  the  part  of  peripheral  mechanical 
elements  to  assume  a  more  central  position,  hence  from  a  morpho- 
logical point  of  view  they  have  a  resemblance  to  roots.  The  large 
number  of  phenomena  belonging  to  the  domain  of  plant  mechanics, 
which  SCHWENDENER  has  so  faithfully  studied,  cannot  be  fully  dis- 
cussed here.  Two  things,  however,  remain  to  be  mentioned.  Cer- 
tain rhizomes  living  in  very  moist  soil  have  the  outer  parenchyma 
supplied  with  air-spaces,  since  they  are  mostly  surrounded  by  water ; 
collapsing  of  this  tissue  is  prevented  by  a  thin  peripheral  layer  of 
bast-cells.  The  supporting  roots  mentioned  above  (Zea  Mays)  show 
almost  an  equal  distribution  of  mechanical  elements,  so  that  these 
roots  are  midway  between  typical  supporting  organs  and  flexible 
organs. 

In  such  flexible  expanded  organs  as  the  leaves  the  mechanical 
cell-complexes  are  in  two  layers,  one  for  each  surface ;  this  is  in 
accordance  with  the  mechanical  principles  explained  above  (coin- 
pare  Fig.  41). 

It  must  not  be  forgotten  that  thin-walled  turgescent  tissues 
represent  a  more  or  less  firm  substance,  and  in  suitable  positions 
(for  example,  at  opposite  sides  of  a  vascular  cylinder,  or  as  filling 
material  around  the  vascular  bundles)  it  very  materially  assists  in 
increasing  the  flexibility  or  firmness  of  plant-organs. 


TISSUES  AND   SIMPLE  ORGANS  69 

I  have  attempted  to  explain  in  a  few  sentences  with  the  aid  of 
the  figures  the  mechanical  principles  involved  in  the  anatomical 
structure  of  plants,  yet  careful  consideration  will  show  that  the 
magnitude  of  the  entire  mechanical  arrangement  of  plants  may  be 
measured  thereby.  Countless  millions  of  plant-organs  are  subor- 
dinated to  the  above-mentioned  principles.  It  must  also  be  remem- 
bered that  in  the  discussion  of  the  vascular  system  we  must  again 
and  again  recur  to  this  subject.  Some  related  phenomena  are  yet 
to  receive  special  consideration. 

Decrease  in  the  Firmness  of  Flexible  Organs  in  an  A.cropetal 
Direction. — It  would  be  erroneous  to  conclude  that  monocotyledons, 
in  distinction  to  dicotyledons  and  conifers,  were  equally  thick  above 
and  below,  since  they,  as  a  rule,  have  no  secondary  growth  in  thick- 
ness by  means  of  a  cambium  ring.  The  study  of  a  grass-stem  will 
show  this.  In  the  majority  of  monocotyledons  the  rejuvenescence 
upward  of  the  rnonocotyledonous  stem  is  to  be  ascribed  to  different 
causes  from  those  producing  rejuvenescence  in  the  stem  of  dicoty- 
ledons. If  the  expression  "  becoming  thinner  above  "  were  changed 
to  "  becoming  thicker  below,"  we  would  find  that  it  would  be  more 
applicable  to  dicotyledons  than  to  monocotyledons.  It  suggests 
that  among  monocotyledons  the  apical  area  (vegetative  point)  has 
already  become  somewhat  "  firm  "  before  any  considerable  growth 
in  length  takes  place.  The  development  of  the  stem  of  a  palm  is 
quite  different  from  the  development  of  the  stem  of  a  dicotyledo- 
nous tree,  although  rejuvenescence  proceeds  upward.1  This  rejuve- 
nescence, and  especially  the  weakening  of  the  mechanical  system 
toward  the  apex,  is  of  great  importance.  That  this  is  desirable 
can  readily  be  explained  from  a  mechanical  standpoint.  A  hori- 
zontal beam  of  equal  thickness  throughout  and  fastened  at  one 
end  will  break  at  the  point  of  attachment  if  too  great  a  weight  is 
brought  to  bear  upon  the  free  end.  The  point  of  attachment  is 
first  to  give  way,  since  there  the  power  arm  is  longest.  If  a  girder 
is  to  have  no  weakest  point,  there  must  be  a  gradual  increase  in 
firmness  (to  be  determined  mathematically)  toward  the  fulcrum  or 
point  of  attachment.  In  its  perfect  form  we  speak  of  a  "  girder 
of  equal  resistance."  RODENSTEIN  2  at  SCHWENBENER'S  suggestions 


1  Eicbler,  Growth  in  Thickness  of  the  Stems  of  Palms,  Sitzungsber.  der  Ber- 
liner Akademie,  1886. 

2  Structure  and  Life  of  Plants,  III  Vereinschrift  der  "  Gorres-Gesellschaf  t " 
filr  1879. 


70  COMPENDIUM  OF  GENERAL  BOTANY. 

carried  on  some  researches  in  which  lie  demonstrated  the  presence 
of 'such  perfect  mechanical  structures  among  plants. 

Localized  Function  of  Mechanical  Cells. — Phytotomy  reveals 
numerous  instances  of  the  appearance  of  mechanical  cells  and  cell- 
complexes  which  have  nothing  to  do  with  the  flexibility  and  tractive 
resistance  of  organs.  The  general  physiology  of  tissues  in  con- 
junction with  mechanics  will  give  the  desired  explanation  of 
their  existence.  They  evidently  serve  as  a  protection  to  the  ele- 
ments which  conduct  food  substances.  The  layers  of  mechanical 
cells  which  are  frequently  found  closely  associated  with  the  deli- 
cate tissues  which  conduct  albumen  and  other  substances  ("lep- 
tome-bundles ")  are  essentially  protective  in  function.  Let  this 
explanation  suffice  for  the  present.  We  will  again  refer  to  this 
subject  in  the  discussion  of  the  protective  sheath  (endoderm,  inner 
derm  is). 


IY.  THE  FUNCTION  OF  THE  CONDUCTING  SYSTEM. 

A  careful  study  of  the  few  figures  illustrating  the  mechanical 
tissue-system  will  show  that  the  description  of  the  anatomical  struc- 
ture of  the  stem,  root,  and  leaves  would  be  imperfect  if  only  refer- 
ence were  made  to  the  mechanical  tissues  involved.  We  must  also 
discuss  the  conducting  tissue-system. 

We  shall  at  the  same  time  treat  of  the  anatomy  of  the  vascular 
system  and  of  the  mechanical  system,  showing  the  respective  arrange- 
ments of  the  two  in  the  great  plant-groups.  We  shall  study  the 
more  important  organs  in  which  they  occur. 

Consideration  of  the  Conducting  System  in  Itself  and  in  its 
Relation  to  the  Mechanical  System. 

(a)  The  Various  Cell-forms. 

NAGELI,*  in  his  researches  in  plant  anatomy,  introduced  names 
for  plant-tissues  which,  according  to  our  present  knowledge  of  the 
subject,  have  become  in  part  useless.  The  writer  intends  to  give  a 
lucid  presentation  of  the  subject  according  to  the  present  status 


Beitrage  zur  wissenschaftlichen  Botanik,  1858. 


TISSUES  AND  SIMPLE  ORGANS.  71 

of  scientific  botany,  and  not  an  elementary  presentation.  For  that 
reason  we  must  enter  somewhat  into  a  discussion  of  the  progress  of 
botanical  science  as  well  as  of  the  modern  change  of  opinions. 
This  is  important  because  every  modern  author  of  a  work  on  general 
plant  anatomy  must  harmonize  his  position  with  NAGELI'S  concep- 
tions of  "  xylem  "  and  u  phloem." 

SCHWENDENER'S  investigations  of  the  mechanical  tissue-system, 
and  the  attempt  made  to  introduce  gradually  an  anatomical-physio- 
logical terminology  lessened  the  importance  of  Nageli's  terms,  per- 
haps denied  them  the  right  of  existence.  In  spite  of  this  Nageli's 
terms  are  still  in  use,  and  variously  applied  by  different  authors. 

NAGELI  proceeded  from  the  cambium-ring  of  dicotyledonous 
plants,  which  grows  outwardly  and  inwardly,  therefore  showing  a 
bipolar  cell-activity.  From  a  purely  topographical  standpoint  he 
called  the  outwardly  formed  product  phloem  and  the  inwardly 
formed  product  xylem.  By  applying  these  conceptions  to  plant- 
groups  without  a  cambium-ring  confusion  arose.  It  could  not 
be  otherwise.  At  present  we  are  certainly  too  far  advanced  in  our 
knowledge  of  tissues  to  wish  to  divide  them  topographically. 
Earlier  anatomists  subsequent  to  NAGELI  observed  the  occurrence 
of  mechanical  cells  outside  of,  as  well  as  within,  the  cambium-ring ; 
these  authors  did  not  all  agree  with  Nageli  to  designate  similar 
elements  by  different  names.  Further,  we  very  frequently  find 
anatomical  elements  resembling  very  closely  those  occurring  in  the 
phloem  and  xylem,  namely,  the  thick-walled  prosenchy ma-fibres  of 
monocotyledons,  which  occur  as  rings,  ribs,  etc.,  and  are  independent 
of  any  cambium-ring.  One  investigator  may  name  them  "  hard 
bast,"  another  "  woody  cells,"  both  would  be  equally  correct  from 
an  anatomical  standpoint.  LINK  and  KIESER  (earlier  anatomists) 
pronounced  the  mechanical  ring  of  Liliacece  and  other  monocoty- 
ledons to  be  "  bast " ;  MOHL  questioned  the  propriety  of  doing 
so.  DIPPEL  named  the  bast  occurring  in  the  vascular  bundle 
"wood,"  that  occurring  outside  of  the  bundle  bast,  though  the 
cell-forms  are  exactly  alike.  SCHACHT  and  UNGER  do  likewise,  but 
the  former  questions  whether  the  term  wood  is  here  rightly  ap- 
plied.1 

The  author  of  this  book  is  in  a  position  to  make  clear  the  absurd- 
ity of  the  earlier  conceptions  of  Nageli.  I  may  also  refer  to  DE 


Compare  Schwendener's  Mechanische  Priucip. 


72  COMPENDIUM  OF  GENERAL  BOTANY. 

BARY'S  (1877) l  attempt  to  introduce  a  scientific  terminology,  which 
HABERLANDT(1879)2  strictly  adhered  to  and  embodied  in  his  writ- 
ings. At  the  present  time  there  is  no  author  in  Germany  prepared 
to  offer  a  generally  acceptable  terminology  of  tissues  which  could 
be  introduced  in  a  manual  of  botany.  The  best  means  of  making 
one's  self  understood  and  of  offering  something  useful  to  the  begin- 
ner in  scientific  botany  is,  according  to  my  opinion,  the  following: 
One  must  revert  to  the  expressions  which  had  their  origin,  in  part, 
with  the  older  anatomy,  and  which  designated  definite  cell-forms, 
such  as  "  vessels,"  "  tracheids,"  "  wood-parenchyma,"  tl  medullary 
rays,"  "  thick-walled  bast,"  "  libriform-tissue,"  and  "  sieve-tubes  " 
as  "cambiform"  and  "conducting  cells"  ;  and  further,  it  must  be 
established  that  there  are  (1)  water-conducting  elements,  namely 
vessels  and  tracheides ;  (2)  mechanical  elements :  bast-cells  and 
bastlike  cells ;  the  latter  when  occurring  within  the  cambium-ring 
were  already  named  "  libriform "  by  earlier  anatomists ;  (3)  ele- 
ments which  conduct  carbohydrates  (or  physiologically  similar  sub- 
stances):  wood-parenchyma  with  medullary  rays;  (4)  albumen-con- 
ducting elements  :  sieve-tubes  with  cambiform  and  conducting  cells. 

These  cell-forms  (1-4)  designated  by  definite  names  must  be 
clearly  distinguished.  We  shall  now  briefly  consider  their  anatom- 
ical characteristics,  which  are  already  partly  known  from  what  has 
gone  before. 

In  the  mature  state  the  vessels  and  tracheids  are  dead  elements, 
since  they  are  without  a  primordial  utricle.  Vessels  are  generally 
tubes  resulting  from  cell-rows  whose  transverse  walls  have  either 
entirely  or  partially  disappeared  (reabsorbed),  leaving  ridges,  or 
rings,  and  whose  longitudinal  walls  are  strengthened  by  various 
thickenings  (compare  cell-structure).  Tracheids  are  closed  prosen- 
chymatous  dead  cells  whose  walls  resemble  those  of  the  vessels. 
There  are  "  spiral,"  "  reticular,"  ll  scalariform,"  and  "  porous"  tra- 
cheids. Porous  tracheids  are  particularly  numerous ;  they  usually 
have  the  form  of  typical  prosenchyrna-cells,  and  may  be  named 
fibrous  tracheids  as  distinguished  from  the  large-celled  vessel-like 
tracheids.  We  have  already  learned  to  know  the  typical  mechanical 
cells  (Fig.  38)  as  thick-walled  prosencby ma-fibres  with  delicate  linear 
pores  which  usually  extend  diagonally.  While  the  large-celled 


1  Comparative  Anatomy,  p.  330,  et  seq. 
2Entwickelungsgeschickte  des  mechauischen  Gewebesystems. 


TISSUES  AND  SIMPLE  ORGANS.  73 

tracheids  closely  resemble  the  vessels  in  structure,  the  fibrous  or 
long-celled  tracheids  represent  a  form  intermediate  between  me- 
chanical cells  and  tracheal  elements.  The  fibrous  tracheids  are 
therefore  dead  prosenchy  ma-cells  with  numerous  bordered  pores. 
They  occur  very  abundantly  in  the  wood  of  conifers ;  they  are 
also  frequently  intermingled  with  the  various  tissue-elements  of 
angiospermous  trees.  The  term  "  bordered  -porous  -libriform " 
is  sometimes  used  to  designate  these  tracheids ;  this  term  is  in- 
tended to  imply  that  they  resemble  mechanical  cells  in  structure 
and  function,  but  that  they  differ  from  specific  mechanical  cells 
(bast-cells  and  libriform-cells  of  trees)  in  having  no  bordered  pores, 
but  only  such  without  borders.  The  absence  of  the  primordial 
utricle  in  the  mature  libriform  is  not  a  characteristic  of  this  cell- 
form,  although  it  is  frequently  spoken  of  as  a  dead  tissue,  and  this 
with  some  degree  of  justification.  Woody  parenchyma  and  medul- 
lary rays  are  physiologically  equal  in  so  far  as  both  consist  of  living 
cells  which  at  definite  periods  carry  considerable  carbohydrate  as 
well  as  physiologically  related  substances ;  anatomically  they  also 
resemble  those  parenchymatous  cells  having  numerous  rounded 
simple  pores ;  they  differ,  however,  in  their  position  and  arrange- 
ment. Woody  parenchyma  usually  extends  longitudinally  in  the 
form  of  bundles  or  bands ;  sometimes  it  slants  in  a  tangential  or 
radial  direction.  Medullary  rays  represent  radial  bands  or  plates 
having  the  form  of  cell-surfaces  or  expanded  cell-complexes.  The 
individual  cell  of  the  wood- parenchyma  is  regularly  elongated  in 
direction  of  the  axis  of  growth ;  the  cell  of  the  medullary  ray  is 
elongated  in  a  radial  direction,  at  least  very  frequently.  The  func- 
tion of  conduction  is  not  only  assisted  by  this  special  arrangement 
of  the  wood-parenchyma  and  medullary  ray,  but  also  by  the  numer- 
ous pores  occurring  in  the  most  suitable  parts  of  the  cell-walls.  In 
the  medullary  rays  the  pores  are  therefore  most  numerous  in  the 
tangential  walls.  (Cell-forms  intermediate  between  wood-paren- 
chyma and  libriform  are  named  "substitute  fibres"  (Ersatzfaserri) 
by  SA^IO.)  A  more  or  less  theoretical  observation  may  be  intro- 
duced here,  namely,  that  cells  resembling  wood-parenchyma  also 
occur  outside  of  the  cambium  between  the  cortical  medullary  rays. 
This  might  be  a  reason  why  the  term  "  woody  parenchyma  "  should 
be  rejected,  since  this  cell-form  occurs  not  only  in  the  woody  paren- 
chyma, but  also  in  the  inner  cortical  tissue,  as  well  as  within  and 
also  outside  of  the  monocotyledonous  vascular  bundles.  But  because 


74  COMPENDIUM  OF  GENERAL  BOTANY. 

of  the  fact  that  the  term  has  become  firmly  rooted  and  that  it  is 
used  with  some  degree  of  justification  such  a  procedure  is  not  ad- 
visable. It  should,  however,  be  observed  that  wood-parenchyma 
and  medullary  rays  together  form  an  anatomical-physiological  system. 
From  this  standpoint,  therefore,  the  ray-parenchyma  cells  and  the 
wood-parenchyma  cells,  whether  they  occur  within  or  outside  of  the 
cambium,  may  be  named  alike,  as  is  likewise  done  in  the  case  of  the 
mechanical  cells.  According  to  the  proposition  advanced  by 
TKOSCHEL  (1879),  a  pupil  of  SCHWENDENER,  the  entire  conducting- 
parenchyma  (medullary-ray  tissue  and  longitudinal  bundle-paren- 
chyma) contained  in  the  conducting  bundles  might  be  designated 
as  "amylome."  To  me  the  term  fascicular  conducting -paren- 
chyma seems  to  be  preferable,  since  it  at  the  same  time  points  out 
the  important  fact  that  there  is  also  an  extra-fascicular  conducting- 
parenchyma,  namely,  the  parenchyma  of  the  vascular  bundle-sheaths 
(in  leaves,  petioles,  etc.),  and  the  cortical  parenchyma  of  stems  and 
petioles.  As  already  stated,  these  structures  are  concerned  with  the 
circulation  of  carbohydrates  and  physiologically  related  substances, 
such  as  inulin,  etc. 

(  Finally,  we  will  briefly  mention  the  sieve-tubes  with  the  cam- 
"biform  and  conducting-cells.  The  fundamental  characteristic  of  this 
tissue  is  softness,  whether  the  cell-walls  are  thin  or  comparatively 
thick.  The  ultimate  anatomical -physiological  difference  between 
,  cambiform  and  conducting  cells  must  now  be  more  clearly  defined.1 
These  tissues  afford  a  difficult  study  when  considered  from  the 
point  of  mere  anatomical  description.  Sieve-tubes  are  usually  elon- 
gated cells  with  rather  thick,  sometimes  thin,  longitudinal  walls  and 
horizontal  or  diagonal  transverse  walls ;  the  latter,  sometimes  also 
the  longitudinal  walls,  contain  minute  perforations.  These  thin, 
perforated  cell-wall  areas  are  designated  sieve-plates  or  sieve-disks. 
In  much-inclined  transverse  walls  there  are  usually  several  sieve- 
plates;  in  the  walls  that  are  horizontal  or  only  slightly  inclined  there 
is  usually  only  one.  The  sieve-plates  are  perforated  and  not 
porous.  These  openings  permit  the  circulation  of  undissolved 
mucous  albuminous  substances. 

The  accompanying  figure  (43)  shows  the  structure  of  a  trans- 
verse wall  which  has  been  converted  into  sieve-plates.    'This  figure 


1  See  DE  BARY,  Comparative   Anatomy.     WILHELM,  JANCZEWSKI,  and  other 
authors  have  carried  on  special  researches  concerning  sieve-tubes. 


TISSUES  AND  SIMPLE  ORGANS. 


75 


represents  their  appearance  during  the  summer.  A  noteworthy 
change  takes  place  in  these  sieve-plates  during  the  winter:  the 
entire  sieve-plate  septum  becomes  swollen 
and  softened  on  the  two  surfaces,  similar 
to  a  gelatinous  cell-membrane  ("  callus  "). 
This  callus  evidently  serves  to  close  the 
openings  of  the  sieve-plate  in  the  winter.1 
The  following  table  gives  the  earlier  and 

°fou 


ter  names   <>f   "ell-forms  which  were   in- 
eluded    in     the   old    expression    "  vascular 
bundle."     It  forms  a  fitting  conclusion  to 
the  discussion  of  the  cell-forms  enumerated  in  this  chapter. 


sieve-plates. 


HABEKLANDT'S  Synopsis  of  Cell-forms,  Slightly  Modified  by  the 

Author. 


£ 


r 

r  Sieve-tubes  and  con- 

Leptome  (Haberlandt) 

ducting-cells 

Sieve-portion(del$a,ry),  , 

Cambiform 
Longitudinal  bundle- 

*  Phloem  (Nageli) 

unluckily    named 

parenchyma 

Mestome 

'  '  soft  bast'  '  by  some 

Medullary  -  ray    pa- 

' 

(Sckwen-  - 

renchyma             ,  . 

dener) 

C  Vessels    and    tra-  ^ 

Hadrome  (Haberlandt) 
Vascular    portion    (d< 

cheids 
3  -|    Woody   parenchy- 

Xylem (Nageli), 
usually  called 

Bary) 

ma 

"  wood." 

[  Ray-parenchyma 

..Libriform 

• 

Bast  and  libriform  really  do  not  belong  to  the 
they  form  (inclusive  of  collenchyma)  an  independent  tissue- system, 
the  stereome  (mechanical  system). 

A  small  conducting  system  which  is  not  widely  distributed,  but 
is  limited  to  certain  plant-families,  has  not  yet  been  touched  upon, 
but  will  now  be  briefly  discussed.  This  is  the  laticiferous  tissue 
("  milk-tubes").' 

1  DE  BARY,  Comparative  Anatomy. 


76  COMPENDIUM  OF  GENERAL  BOTANY. 

(b)  The  Laticiferous  Tissue. 

An  important  conclusion  to  the  subject  under  consideration, 
that  is,  the  cell- forms  which  conduct  water  and  food  substances,  is 
the  discussion  of  the  milk- tissue  or  laticiferous  tissue  of  plants. 
The  laticiferous  tubes  occur  most  frequently,  but  not  exclusively, 
in  the  albumen -conducting  tissues  of  the  vascular  bundles ;  they  are 
also  found  in  the  outer  parenchyma  and  in  some  other  tissues. 
This  tissue-system  affords  an  excellent  illustration  of  the  correctness 
of  this  statement :  Different  modes  of  development  produce  physio- 
logically similar  structures.  There  are  :  1,  simple,  2,  complex,  milk- 
tubes.  In  the  mature  state  both  present  the  appearance  of  a  much- 
branched  system  of  canals,  though  even  in  the  earlier  stages  close 
examination  will  reveal  the  distinguishing  characteristics  of  the  two 


a 

FIG.  44. — Laticiferous  vessels  (diagramatic). 
a,  Branching  ;  6,  anastomosing. 

forms  of  tissues.  The  complex  milk-tubes  (Cichoriacece,  Papave- 
racece)  form  a  reticular  structure  by  the  joining  of  many  branches 
("anastomosing");  the  simple  (Euphorbiacece,  Apocynacece^  Mo- 
racece)  tubes  seldom  anastomose,  or  perhaps  not  at  all.  To  deter- 
mine whether  a  given  milk-tissue  is  simple  or  complex  is  one  of  the 
difficult  problems  of  plant- anatomy,  and  conclusions  differ  with 
different  authors. 

The  names  indicate  the  mode  of  development  of  the  two  forms 
of  tissue.  The  complex  milk-tubes  are  cell-fusions  in  which  the 
remnants  of  the  unabsorbed  cell -walls  are  visible  at  the  points  of 
union  (see  Fig.  44,  I).  The  simple  forms  can  be  traced  to  a  few 
milk-cells  which  exist  in  the  embryo  of  the  plant,  and  which  sub- 
sequently grow  in  length  and  branch  in  a  manner  similar  to  the 
hyphse  of  fungi  (Fig.  44,  a).  As  already  stated,  anastomosing  (fu- 


TISSUES  AND  SIMPLE  ORGANS. 


77 


sion)  rarely  or  never  (?)  occurs  in  the  simple  milk-tubes.  There  is 
nothing  definitely  known  concerning  the  physiology  and  movement 
of  the  fluid  within  the  laticiferous  vessels.  The  following  may, 
however,  suffice  to  give  an  idea  of  the  probable  condition  of  affairs : 
The  milky  fluid  is  composed  mainly  of  water,  fats,  starch,  tannin, 
and  grains  of  resin ;  it  is  usually  white,  more  rarely  yellow  or  red. 
Observations,  even  those  of  a  purely  comparative  character,  indi- 
cate that  the  milk-tubes  obtain  at  least  their  carbohydrates  from 


FIG.  45. — Cross-section  of  the  stem  of  Selaginella  incequalifolia. 
(x!50.)    (After  Sachs.) 

the  centres  of  assimilation,  namely,  from  the  palisade- cells  of  the 
leaves.  The  fact  that  the  milk-sap  sometimes  becomes  watery,  for 
example,  when  seeds  germinate  in  the  dark,  would  seem  to  indi- 
cate that  it  is  a  formative  substance.  In  certain  cases  it  has  been 
observed  that  the  presence  of  milk-tubes  in  leaves  corresponded  to 
a  diminution  of  the  conducting-parenchyma  of  the  vascular  bundle. 
In  reference  to  the  movements  of  the  milk-sap  we  must  make  a 
distinction  between  thick-walled,  and  thin-walled  milk-tubes.  In 
the  latter  it  is  essentially  the  hydrostatic  pressure  of  the  surround- 


78 


COMPENDIUM  OF  GENERAL  BOTANY. 


4ng  cells  that  causes  the  movement ;  in  the  former  the  elastic  force 
of  the  walls  themselves  is  brought  into  requisition  (SCHWENDENEK). 
Physiology  leaves  it  an  open  question  whether  or  not  milk-sap  also 
contains  products  which  are  useless  in  the  further  processes  of  nu- 
trition. Milk-sap  may  also  serve  collateral  functions.  The  sap 
escaping  from  injured  tissues  forms  an  air-tight  protective  coating. 


FIG.  46. — Smaller  vascular  bundle  of  the  rhizome  of  Polypodium  glaucophyllum. 

(After  Potoni6.) 

The  questions  relating  to  the  function  and  use  of  milk-sap  require 
further  study,  however. 

Having  now  obtained  a  knowledge  of  the  cell-forms,  we  shall 
next  proceed  with  the  anatomical  (in  part  also  the  developmental) 
and  physiological  discussion  of  the  chief  plant-organs  of  the  entire 
vegetable  kingdom,  beginning  with  the  mosses. 

(c)  The  Stem- Structure  of  Mosses  and  Vascular  Cryptogams. 

In  the  stem  of  mosses  (example,  Polytrichum)  the  central 
bundle  of  thin-walled  cells  represents  the  vascular  system ;  a  strictly 
peripheral  ring  of  thick-walled  cells  functions  as  the  mechanical 
system  (HABEKLANDT.)  1 


1  Beitrage  zur  Anatomic  und  Physiologic  der  Laubmoose,  Pringsheim's  Jahr- 
biicher,  1886. 


TISSUES  AND  SIMPLE  ORGANS.  79 

A  cross-section  of  the  stem  of  a  vascular  cryptogam  (Selaginella 
incequalifolia)  may  also  serve  to  show  the  structural  relations  of 
the  upright  and  semi-upright  (hence  more  or  less  firm  and  elastic) 
stems  of  the  fern-leaves. 

Fig.  45  represents  the  peripheral  mechanical  ring  of  the 
stem.  In  the  centre  lie  three  vascular  bundles  surrounded  by  a 
loose  connective  tissue  with  large  intercellular  air-spaces.  We  can 
now  also  understand  the  structure  of  a  single  vascular  bundle  of  a 
fern  (see  Fig.  46),  which  in  many  respects  resembles  that  of  Sela- 
ginella. The  leptome  in  the  form  of  two  crescents  lies  in  contact 
with  the  plate  consisting  of  woody  parenchymatous  and  tracheal 
elements;  the  fascicular  conducting-parenchyma  s  surrounds  the 
albumen-conducting  elements  in  the  form  of  a  ring.  The  protect- 
ive sheath  is  shown  at  <?,  the  strengthening  layer  at  w.  I  wish  to 
state  at  this  point  that  according  to  more  recent  investigators  the 
majority  of  vascular  cryptogams  do  not  possess  a  true  vascular  sys- 
tem ;  the  tracheal  elements,  in  most  cases,  prove  to  be  tracheids. 

Furthermore,  in  the  group  of  vascular  cryptogams  there  is 
represented  a  wholly  different  type  of  structure ;  this  type  is  well 
illustrated  in  the  Equisetacece.  For  special  functions,  and  hence 
explanatory  from  a  physiological  standpoint,  the  stem  of  Equise- 
tum  has  an  essentially  different  structure  from  the  stem  of  Sela- 
ginella and  the  leaf-stems  of  related  ferns.  On  account  of  the 
rudimentary  leaf -development  among  the  Equisetacece,  assimilation 
on  the  part  of  the  leaf  is  almost  zero ;  only  the  toothed  leaf-sheaths 
are  present,  and  these  function  at  the  same  time  as  mechanical 
structures.  The  stem  with  its  branches  must  therefore  perform 
the  function  of  assimilation.  To  suit  this  requirement  the  mechan- 
ical and  assimilating  systems  are 
alternately  arranged  on  the  outer 
surface.  A  glance  at  Fig.  47  will 
explain  this  arrangement.  Be- 
tween the  bast-ribs  (black)  lie  the  " 

.     . ,  FIG.  47. — Transverse  section  of  the 

assimilating    tissues   gr ;     inside    of          stem  of  Equisetum  htemale. 
the  bast-ribs  are  found  the  conduct-  (Diagramatic.) 

ing  bundles  Z,  and  between  these  the  large  intercellular  air-pas- 
sages. (This  figure  also  illustrates  the  rare  case  of  an  inner  and  an 
outer  ' '  protective  sheath, ' '  concerning  which  more  particular  men- 
tion will  be  made  later.  The  dotted  lines  indicate  their  courses.) 


80  COMPENDIUM  OF  GENERAL  BOTANY. 

(d)  The  Stem  of  Monocotyledons,  Dicotyledons,  and 
Gymnosperms. 

Elementary  treatises  on  the  stem- structure  of  the  great  divisions 
of  monocotyledons  and  dicotyledons  emphasize  two  distinctive 
characters,  namely,  that  monocotyledons  in  general  do  not  essen- 
tially grow  in  thickness,  that  their  ' '  closed ' '  vascular  bundles  are 
scattered  through  the  stem  as  seen  in  cross- section ;  on  the  other 
hand  dicotyledons  grow  in  thickness  by  means  of  a  cambium 
and  their  ' 4  open  ' '  vascular  bundles  are  arranged  in  the  form  of  a 
ring,  as  shown  in  cross-section.  Further  investigations  will  of 
course  reveal  other  differences. 

The  normal  monocotyledonous  stem  is  formed  differently  from 
the  normal  dicotyledonous  stem.  In  the  palm  the  young  plant  in 
its  earliest  stages  of  development  forms  a  structure  of  considerable 
diameter ;  upon  this  the  stem  is  subsequently  elongated  similarly  to 
the  building  of  a  tower  ;  a  more  or  less  embryonic  condition 
toward  the  apex  is  not  excluded.  The  dicotyledonous  stem,  for  ex- 
ample— maple,  grows  to  a  considerable  length  during  the  first  year ; 
during  the  second  year  it  adds  to  this  length  and  also  grows  in 
thickness  at  the  basal  portion  according  to  the  mechanical  require- 
ments ;  that  is,  it  nas  the  ability  to  surround  the  stem  of  the  first 
year's  growth  with  a  second  annual  ring;  during  the  third  year  an 
additional  ring  is  formed  around  the  second  year's  growth,  and 
BO  on  for  a  number  of  years  ;  therefore  the  base  of  the  tree  in- 
creases in  thickness,  and  hence  in  strength,  corresponding  to  the 
increase  in  height.  ( Gymnosperms'  grow  in  a  similar  manner.) 

It  is  well  to  note  the  fact  that  the  specific  mechanical  elements 
of  dicotyledons  and  of  monocotyledons  are  differently  united  with 
the  conducting  elements.  In  the  latter  the  mechanical  elements 
and  the  conducting  elements  are  either  entirely  separated  or  are 
placed  in  juxtaposition. 

The  comparison  of  the  two  great  plant-groups  suggests  still 
another  thought.  If  one  recalls  the  mechanical  principles  which 
underlie  the  arrangement  of  mechanical  elements  in  the  firm  organs, 
and  if  we  study  a  cross-section  of  an  oak  or  conifer,  the  idea  must 
suggest  itself  that  rational  constructive  principles  from  a  purely 
mechanical  standpoint  are  wholly  out  of  the  question ;  for  we  have 
here,  leaving  out  of  consideration  the  small  amount  of  pith,  almost 


TISSUES  AND  SIMPLE  ORGANS.  81 

a  solid  cylinder  of  wood,  and  not  a  hollow  cylinder,  which  is  the 
type  of  a  perfect  mechanical  construction.  In  fact,  SCHWENDENER 
would  probably  not  have  succeeded  in  proving  that  dicotyledons 
as  well  as  monocotyledons  have  a  specific  mechanical  tissue-system. 
It  must  be  remembered  that  in  dealing  with  dicotyledons  and  coni- 
fers we  are  concerned  with  living  plants,  and  not  with  dead  models 
or  types  for  mechanical  engineers.  The  anatomist  knows  that  the 
older  rings,  and  hence  a  part  of  the  inner  mass  of  the  wood  (see 
heart-wood),  at  least  up  to  a  certain  age,  serve  a  wholly  dif- 
ferent function  from  that  of  pure  mechanics ;  they  contain  living 
elements,  namely,  wood-parenchyma  and  medullary  rays,  which 
bear  starch  during  the  winter  months.  The  function  of  storing 
reserve  food-substances,  concerning  which  more  will  be  said  later, 
is  here  of  prime  importance.  Furthermore,  since  it  is  generally 
known  that  the  woody  plants  of  the  geologic  ages,  as  well  as  those 
of  the  present  time,  are  of  inestimable  value  to  mankind,  no  one 
need  hesitate  in  expressing  the  opinion  that  there  is  a  general 
manifestation  of  a  purposeful  relation  of  the  various  organic  king- 
doms. Such  relations  are  also  observed  in  other  domains. 

Let  us  now  proceed  farther  with  the  discussion  of  the  anatomical 
differences  between  the  monocotyledonous  stem  and  the  stem  of 
dicotyledons  as  well  as  that  of  conifers. 

The  Arrangement  of  Vascular  Bundles.1 — In  the  monocoty- 
ledonous stem  the  vascular  bundles  lie  isolated  in  the  fundamental 
tissue ;  in  the  dicotyledonous  stem  they  form  a  cylindrical  mantle 
fused  with  the  cambium.  The  apparent  promiscuous  distribution 
of  the  vascular  bundles  of  monocotyledons  must  not  be  considered 
as  being  of  any  special  importance :  an  arrangement  in  a  series  of 
circles,  for  example,  is  frequently  noticed.  We  may  designate 
as  fundamental  tissue  (in  partial  agreement  with  SACHS)  that 
which  remains  after  the  epidermal  tissues,  the  mechanical  and  the 
conducting  elements,  have  been  removed ;  hence  the  tissue  in  which 
the  mechanical  and  the  conducting  bundle-elements  seem  to  be 
imbedded. 

The  individual  bundle  in  the  mature  monocotyledonous  stem 
has  no  cambium  (long-celled  prosenchymatous  formative  tissue) 

1  Recent  authors  still  use  this  expression  in  the  same  sense  as  did  the  older 
authors,  namely,  for  tissue-bundles  which  consist  of  conducting  elements  as  well 
as  of  mechanical  elements. 


b2  COMPENDIUM  OF  GENERAL  BOTANY. 

even  at  a  very  short  distance  from  the  primary  meristem  of  the 
apex.  The  typical  dicotyledonous  bundle  possesses  cambium  dur- 
ing its  entire  life-period.  The  elements  of  the  vascular  bundles 
of  the  monocotyledons  also  had  their  origin  from  cambium,  but 
the  formative  tissue  soon  becomes  changed  into  permanent  tissue- 
elements,  and  in  regard  to  the  individual  bundle  this  change  pro- 
ceeded centripetally  ;  the  sieve-tube  tissue  (leptome)  and  the  ves- 
sel-bearing portion  (hadrome)  with  the  accompanying  mechanical 
cells  lie  in  close  proximity.  In  dicotyledons  and  conifers  the  cor- 
responding tissues  —  namely,  the  secondary  cortex,  which  is  formed 
outwardly  by  the  cambium,  and  the  wood,  formed  inwardly  —  are 
always  separated  by  the  cambium.  In  winter  there  is  at  least  one 
cell-layer  of  the  cambium,  which  represents  the  separating  boundary 
between  the  cortex  and  wood.  The  cortex,  which  is  formed  from 
the  first  or  primary  meristem  of  the  stem-apex,  and  which  there- 
fore existed  before  the  appearance  of  the  cambium-ring,  is  called 
primary  cortex,  in  distinction  to  the  cortex  formed  by  the  cambium. 
It  does  not  show  the  characteristic  radial  structure  seen  in  the  sec- 
ondary cortex. 

The  customary  way  of  speaking  of  the  monocotyledonous  bun- 
dles as  '  '  closed  '  '  and  those  of  dicotyledons  as  4  '  open  '  '  is  rather 
unfortunate,1  for  the  monocotyledonous  bundles  are  opened  toward 
the  fundamental  tissue  by  means  of  special  structural  arrangements 
(transit-cells,  large  thin-  walled  cells,  etc.),  while  the  dicotyledo- 
nous bundles  form  a  closed  complex  by  means  of  the  cambium,  so 
that  the  individual  bundle  is  scarcely  recognizable  as  such.  There- 
fore the  fundamental  tissue  of  dicotyledons  and  conifers  is  plainly 
divided  into  cortex  and  parenchyma  (medulla),  a  peripheral  and  a 
central  portion,  which  have  an  anatomical-physiological  connec- 
tion through  the  medullary  rays.  In  monocotyledons  the  boundary- 
line  between  cortex  and  medulla  is  also  often  well  marked,  at  least 
in  the  numerous  cases  in  which  the  bast-ring  represents  the  me- 
chanical system.  From  some  statements  made  by  SCHWENDENER 
on  p.  71  of  his  '  '  Mechanische  Princip  "  it  would  seem  that 
such  demarcation  between  the  cortex  and  the  medulla  of  mono- 
cotyledons without  a  bast-  ring  is  not  easily  demonstrated.  With 
regard  to  the  radially  diagonal  course  of  many  leaf  -bundles  in  mon- 


designated  the  monocotyledonous  bundles  not  as  "closed,"  but  as 
"  enclosed,"  which  is  more  nearly  correct. 


TISSUES  AND  SIMPLE  ORGANS. 


83 


ocotyledons,  SCHWENDENER  has  designated  as  cortex  that  periph- 
eral portion  in  which  the  leaf-traces  (the  vascular  bundles  enter- 
ing from  the  leaves)  in  their  course  downward  extend  diagonally 
inwrard  or  parallel  with  the  outer  surface.  As  a  result  the  inner 
boundary  of  this  cortex  does  not  form  a  smooth,  even  surface :  it 
is  rather  a  cylindrical  surface  with  numerous  projections. 

This  leads  to   the  discussion  of  the   arrangement  of  vascular 


FIG.  48. — Arrangement  of  the  vascular  bundles  in  Sedum  reflexum.    (After  Teitz.) 

Each  one  of  the  spirally  arranged  leaves  appears  with  its  vascular  system,  as  indicated  by  the 
numbers.  This  figure  also  has  a  bearing  upon  the  subsequent  discussion  of  the  mechan- 
ical influence  which  the  position  of  mature  leaf-bundles  in  the  stem  has  on  the  position  of 
young  leaves. 

bundles  in  the  stem  and  in  other  organs.     We  shall  begin  with  the 
stem,  and  allude  to  the  most  important  facts  only. 

Among  dicotyledons  the  leaf-bundles  usually  extend  radially 
vertical.  In  most  monocotyledons  the  numerous  leaf -traces  of  each 
leaf  do  not  all  take  the  same  course.  The  median  leaf -bundles  ex- 
tend most  deeply  into  the  stem,  describing  a  curve  upon  the  radial 


84 


COMPENDIUM  OF  GENERAL  BOTANY. 


plane ;  those  bundles  placed  in  a  somewhat  more  lateral  position 
penetrate  less  deeply  and  describe  a  smaller  curve ;  those  still  more 
lateral  enter  least  deeply  and  soon  extend  vertically  downward, 
In  monocotyledons  the  course  of  the  vascular  bundles  in  the  tan- 
gential plane  may  be  described  as  follows :  Each  radially  curved 
bundle  inclines  in  a  tangential  direction.  Among  dicotyledons  a 
tangentially  inclined  course  of  the  vascular  bundles  is  the  rule ; 
they  unite  laterally  after  they  have  taken  an  isolated  course  down- 
ward for  some  distance.  Fig.  48  represents  the  tangentially  in- 
clining course  of  the  leaf-bundles  of  Sedum  reflexum  (dicotyledon) 
upon  the  surface  of  a  cylinder. 

There  is  a  leaf  at  every  node  and  every  leaf  contains  vascular 
bundles.  The  radially  diagonal  course 
of  the  vascular  bundles  in  monocotyle- 
dons is  shown  in  Fig.  49,  which  is  a  dia- 
gramatic  median  longitudinal  section. 
Only  a  few  of  the  leaf-bundles  are  rep- 
resented in  order  to  illustrate  the  rela- 
tions explained  above.  The  dotted  lines 
are*  intended  to  show  the  tangentially 
inclined  course  of  the  radially  curved 
bundles.  The  arrangement  and  distri- 
bution of  vascular  bundles,  according  to 
the  requirements  of  nutrition,  that  is, 
for  the  uniform  distribution  of  water 
and  of  food-substances,  have  received 
special  attention  from  HABERLANDT.1 
The  numerous  anastomoses  of  vascular 
bundles  in  the  leaves  are  of  great  im- 
portance in  cases  of  local  injury,  in  that 
the  neighboring  bundles  are  thereby  en- 
FlG-  49-  abled  to  take  up  the  work  of  those  de- 

stroyed.    (The  circulatory  system  in  man  is  similarly  arranged.) 

The  following  is  of  importance  in  regard  to  the  arrangement 
and  structure  of  the  vascular  bundles  in  the  leaves.  Green  leaves: 
are  for  the  purpose  of  assimilation.  Therefore  the  mechanical 
elements  must  maintain  these  flattened  organs  in  a  suitable  position 
with  regard  to  the  light  (see  pp.  67  and  68  in  regard  to  the 
1  Phys.  Pflanzen-Anatomie. 


TISSUES  AND  SIMPLE  ORGANS. 


85 


mechanical  tissue — bast — of  the  vascular  bundles) ;  the  conducting 
elements  must  on  the  one  hand  carry  the  necessary  water  and  the 
various  food-substances  to  the  leaves,  and  on  the  other  hand  they 
must  conduct  the  products  of  assimilation  from  the  leaves  to  the 
stem.  As  we  have  already  learned,  the  leptome  in  the  stems  of 
monocotyledons  and  dicotyledons  is  placed  toward  the  outer  sur- 


FIG.  50. — Vascular  bundle  of  the  stem  of  Zea  Mays,     (x  560.) 

v,  Albumen-conducting  tissue,  leptome  or  sieve-tissue  ;  p,  parenchyma  ;  s  and  r,  primordial 
(primary)  vessels  ;  gr,  secondary  vessels  ;  I,  intercellular  space  ;  a,  side  facing  outward ;  i, 
side  facing  inward.  (After  Sachs.) 

face,  the  vascular  portion  toward  the  interior;  corresponding  to 
this  arrangement  we  find  the  leptome  of  the  leaves  near  the  lower 
surface  and  the  hadrome  (vascular  portion)  near  the  upper  surface. 
Occasionally  skeleton-bundles  (mechanical  cells)  which  prevent  the 
tearing  of  leaves  by  strong  winds,  etc. ,  are  brought  into  mechani- 
cal operation ;  these  bundles  are  usually  found  near  the  middle  of 


86 


COMPENDIUM  OF  GENERAL  BOTANY. 


the  leaf,  as  seen  in  cross-section.  Further,  there  are  often  special 
mechanical  cells  at  the  margin  of  the  leaf  which  also  assist  in  pre- 
venting tearing  (SACHS,  HABEKLANDT,  HINTZ). 

Although  the  difference  between  monocotyledons  and  dicotyle- 
dons is  very  great,  we  must  not  omit  to  note  the  similarities  that 
exist.  If  we  leave  out  of  consideration  the  cambium,  we  cannot 
fail  to  see  the  similarity  between  a  rnonocotyledonous  and  a  dicoty- 


FIG.  51. — Vascular  bundle  of  Ricinus  communis. 

6,  Bast ;  |/,  sieve-tissue  or  leptome  ;  g  and  i,  vessels  ;  c  and  cb,  cambium  ;  r,  parenchyma ; 
just  beyond  b  a  starch-bearing  layer  (bundle-sheath).    (After  Sachs.) 

ledonous  vascular  bundle.  The  explanations  of  the  figures  of 
the  rnonocotyledonous  bundles  in  the  text-books  of  SACHS,  HABER- 
LANDT,  FRANK,  and  in  the  plates  of  KNY,  are  imperfect,  since 
the  rather  plentiful  wood-parenchyma  is  scarcely,  or  not  at  all, 
mentioned.  The  tissue  between  the  two  large  vessels  (g)  and  the 
ring- vessels  («,  r  in  Fig.  50),  near  the  sides  between  the  two 
larger  vessels,  are  in  part  wood-parenchyma,  in  part  thick-walled 


TISSUES  AND  SIMPLE  OKGANS.  87 

and  in  part  thin- walled  tissue.  In  both  monocotyledons  and  dicoty- 
ledons (see  figures)  an  imaginary  line  drawn  through  the  stem  in 
cross-section  first  cuts  the  outer  bundle- elements  of  the  albumen- 
conducting  -tissue,  next  the  two  secondary  vessels  and  the  wood- 
parenchyma,  and  finally,  still  more  internally,  the  primordial  vessels 
and  the  thin- walled  wood -parenchyma.  In  both  plant-divisions  the 
primordial  vessels  are  narrower  than  the  secondary  vessels.  The 
mechanical  cells  of  the  vascular  bundle  of  Zea  Mays 
leave  four  passage-ways  between  the  fundamental 
tissue  and  the  interior  of  the  bundle.  The  accom- 
panying diagramatic  figure  (52)  shows  this  much 
better  than  the  figure  of  the  vascular  bundle  of  Zea  . 
Mays,  in  which  the  four  passages  are  scarcely  recog-  / 
nizable.  They  are  indicated  by  an  increase  in  the  FlG'  53< 

J  (Diagramatic.) 

size  of  the  cells.  Since  the  mechanical  (skeleton) 
cells  in  general  do  not  belong  to  the  conducting  bundle,  we  find 
that  they  are  not  present  in  the  hadrome  of  the  .S^cm'ws-bundle, 
but  are  arranged  in  small  groups  near  the  leptome.  In  this 
respect,  however,  the  bundles  of  the  dicotyledonous  stem  differ 
very  frequently. 


(e)   Growth  in  Thickness  among  Dicotyledons  and  Monocotyledons 
~by  Means  of  the  Cambium. 

It  is  important  to  recognize  the  fact  that  the  cambium  of  our 
endogenous  trees  and  shrubs  is  a  bipolar  formative  tissue ;  that  is, 
each  individual  normal  cambium-cell,  when  at  the  height  of  its 
activity,  must  show  :  1,  a  daughter-cell  which  was  cut  off  outwardly ; 
2,  a  daughter- cell  which  was  cut  off  inwardly ;  and  3,  a  cell  lying 
between  the  two  having  the  power  of  again  dividing.  These 
middle  cells  (3)  form  a  cylindrical  covering  (cambium  covering)  in 
the  stems  and  roots.  In  cross-section  this  appears  as  a  ring. 

Growth  in  thickness  of  stems  and  roots  by  means  of  the  cam- 
bium-ring produces  such  characteristic  structural  changes  as  will 
astonish  the  young  anatomist  in  the  examination  of  cross-,  tangential, 
and  radial  sections.  He  will  also  observe  numerous  deviations 
from  the  normal  growth-type.  To  enter  into  a  more  particular 
discussion  of  these  deviations  is  impracticable,  though  it  is  neces- 
sary to  bear  in  mind  that  they  exist.  We  shall  now  enter  into  a 


88 


COMPENDIUM  OF  GENERAL  BOTANY. 


brief  discussion  of  the  characteristic  activity  of   the  cambium-ring 
and  the  typical  appearance  of  various  sections  of  stems  and  roots. 

A  cross-section  shows  the  successive  order  of  the  products  re- 
sulting from  the  cambial  activity,  namely,  the  arrangement  of  the 
wood-elements  on  one  side  of  the  cambium,  and  the  secondary  cortex 
on  the  other  side.  Radial  bands  can  be  traced  from  the  wood 
through  the  cambium  into  the  albumen-conducting  tissue.  It 
should  be  noted  that  the  primordial  arrangement  is,  for  various 
reasons,  very  materially  altered  at  some  distance  from  the  cambium 
(hence  at  a  later  period).  This  secondary  change  consists  mainly 
in  an  increase  in  the  size  of  the  elements  (gliding  growth,  KKABBE), 
and  in  subsequent  divisions  of  the  leptome-elements.  As  a  rule, 
the  radial  structure  is  most  distinctly  shown  in  conifers.  The 


FIG.  53. — Woody  tissue  of  Taxus  baccata  (cross-section). 
g,  Limit  of  the  year's  growth;  m,  medullary  rays.    (After  Haberlandt.) 

cause  for  this  can  readily  be  explained.  Elementary  anatomy 
teaches  that  vessels  are  wanting  in  the  wood  of  conifers.  Macro- 
scopical  examination  of  cross-sections  shows  this  in  the  absence 
of  the  large  vascular  lumina ;  microscopically  this  is  evident  by  the 
large  regularly  arranged  woody  elements  (tracheids  and  medullary 
rays).  Wood-parenchyma  is  rarely  present.  The  following  ele- 
ments bring  about  a  change  in  the  anatomical  appearance  :  1,  resin- 
ducts  ;  they  usually  extend  longitudinally  in  the  sparingly  present 
wood-parenchyma,  or  they  may  extend  radially  in  the  medullary 
ray  tissue ;  2,  the  difference  between  the  growth-products  in  the 
spring  and  in  the  autumn. 

The  latter  morphological  factor  (2)  has  a  bearing  upon  conifer- 
ous wood  as  well  as  upon  dicotyledonous  wood,  and  will  receive 


TISSUES  AND  SIMPLE  ORGANS. 


89 


our  immediate  attention.  Apparently  radially  compressed,  narrow- 
lumened,  thick-walled  elements  mark  off  the  autumn-wood  or 
summer-  wood.  On  the  other  hand  wide-lumened,  thin-  walled, 
radially  elongated,  or,  at  least,  not  radially  shortened,  cell-forms 


FIG.  54. — Section  of  a  ring  of  the  previous  year's  growth.     Cystisus  Laburnum. 

m,  Medullary  rays;  p,  secondary  bark-parenchyma:  ft,  bast;  Z,  leptome;  c,  cambium;  If,  libri- 
form  tissue;   m,  mestome;  g,  year's  limit.     (After  Haberlandt.) 

belong  to  the  spring- wood.  Among  angiospermous  trees  this  con- 
trast is  strongly  marked  by  the  minuteness  or  absence  of  vessels  in 
the  autumn -wood  as  compared  with  the  large  size  and  great  numbers 
of  the  same  in  the  spring- wood.  This  difference,  which  is  usually 


visible  to  the  naked  eye  and  which  marks  off  the 


rings, 


is 


90 


COMPENDIUM  OF  GENERAL  BOTANY. 


supposed  to  be  due  to  an  increased  cortical  pressure  in  the  fall  of 
the  year  (SACHS,  DE  TRIES).  This  assumption  can  no  longer  be 
maintained  in  the  light  of  present  knowledge  of  physiological 
science.1  Even  if  we  were  concerned  only  with  apparent  transfor- 
mations due  to  pressure,  namely,  tangential  spreading,  or  radial  flat- 
tening, this  hypothesis  would  not  be  tenable,  because  of  the  fact  that 
radial  pressure,  in  the  fall,  increases  only  slightly  or  may  even  di- 
minish. However  that  may  be,  it  is  evident  that  the  final  decision 
as  to  whether  a  given  cambium-cell  will  develop  into  libriform, 
wood-parenchyma  cell,  or  a  vessel  with  its  characteristic  thickenings 
of  the  walls,  cannot  simply  depend  upon  a  greater  or  lesser  pressure 
exerted  by  the  cortex.  KKABBE  in  his  first  publication  referring 


FIG.  55. — Medullary  rays  of  Cystisus  Laburnum. 

A,  Large  and  Cm,  small  medullary  rays  in  tangential  longitudinal  section;  Ft  ray  in  radial 
longitudinal  section.    (After  Haberlandt.) 

to  this  subject  questions  rightly :  ' '  Is  the  vessel  perhaps  a  large 
libriform-cell,  or  is  it,  vice  versa,  a  small  vessel?  "  The  annual 
rings  are  not  equally  distinct  in  the  different  trees  and  shrubs. 

A  radial  longitudinal  section  of  dicotyledonous  or  coniferous 
wood  in  surface- view  must  of  necessity  show,  scattered  here  and 
there,  the  medullary  rays  whose  elements  always  cross  the  longitu- 
dinally extending  elements  at  right  angles.  I  can  only  point  out 
the  fact  that  cells  bearing  a  resemblance  to  tracheids  form  the 
medullary  rays  of  some  conifers.  The  length  of  the  medullary  rays, 
their  size  and  the  number  of  cells  in  transverse  direction,  the  origin 

1  Compare  KRABBB,  Tiber  die  Beziehungen  der  Rindenspannung,  etc.,  Sitz- 
imgsber.  der  Berl.  Akad.,  1882.  Also  Krubhe,  Uber  das  Wacbstbum  des  Ver- 
dickungsringes,  etc.,  Abbandl.  der  Berl.  Akad.,  1884. 


TISSUES  AND  SIMPLE  ORGANS. 


91 


of  a  raj  in  the  medulla  and  in  the  primary  cortex  or  at  some  dis- 
tance from  them  ("  primary  "  and  "  secondary  "  medullary  rays), 
the  direction  of  elongation  (stretching)  of  the  cells,  etc.,  produce 
many  changes  in  the  appearance  of  the  plant- structure.  These  and 
similar  anatomical  characteristics  are  also  of  special  interest  to  the 
palaeontologist  in  determining  the  probable  systematic  position  of 
fossil-plants.  Sometimes  the  connection  between  medullary  ray- 
tissue  and  wood- parenchyma  is  very  distinct  and  forms  a  system, 
when,  for  example,  the  wood-parenchyma  cells  form  transverse 
connecting-bands  between  the  medullary  rays.  There  is  another 
phenomenon  which  is  of  frequent  occurrence  and  which  must 


FIG.  56. — Radial  longitudinal  section  of  the  vascular  bundle  in  the  stem  of 
(Enotliera  odorata. 

c,  Cambium;  g,  primordial  vessels.    The  different  forms  of  vessels  will  be  recognized  from 
previous  descriptions.    (After  Haberlandt.) 

receive  special  mention,  though  its  significance  has  only  been  ap- 
proximately determined  from  a  physiological  standpoint,  namely, 
that  the  dead  tracheal  system  and  the  living  cells  (medullary  rays 
and  wood -parenchyma)  form  such  an  intimate  anatomical  relation- 
ship as  to  enable  the  interchange  of  fluids  between  them  (assisted 
by  the  cell-pores).  Further,  we  notice  an  increase  in  the  length  of 
the  mechanical  elements  of  the  woody  body  in  a  direction  from  the 
younger  rings  to  the  older  rings  (hence  from  without  inward). 
Upon  this  perhaps  depends  the  apparent  torsion  of  stems,  that  is, 
the  tangentially  slanting  arrangement  of  the  woody  elements. 

In  regard  to  the  vessels,  a  radial  longitudinal  section  shows  the 
variable  structure  of  the  perforated  transverse  septa  (remnants  of 


92  COMPENDIUM  OF  GENERAL  B01ANY. 

the  cell- walls) ;  they  may  be  scalariform,  reticular,  or  annular.  Tra- 
cheids  have  border  ed-porous  slanting  end -surf  aces ;  this  is  because 
the  originally  transverse  septa  in  the  stem  incline  to  the  right  or 
left.  Fig.  56,  which  represents  a  longitudinal  radial  section  of  a 
dictyoledonous  stem  one  year  old  (CEnotherd)  illustrates  the  im- 
portant difference  between  vessels  which  have  grown  in  length  with 
the  other  tissues  and  those  which  began  development  at  the  close  of 
the  vegetative  period.  Similar  anatomical  relations  also  exist  in 
the  innermost  annual  rings  of  the  dicotyledonous  stems. 

A  tangential  longitudinal  section  again  shows  the  characteristic 
appearances  of  the  medullary  rays.  They  appear  as  two-edged  cell- 
rows  or  cell-groups,  or  as  bands  of  cells  of  one  or  more  layers  in 
thickness,  when  the  ends  are  invisible.  The  typical  appearance  of 
medullary  rays  in  both  longitudinal  sections  (radial  and  tangential) 
is  as  marked  in  the  secondary  cortex  as  it  is  in  the  wood. 

The  difference  between  splint-wood  and  heart-wood  in  dicotyle- 
dons and  conifers  has  long  been  recognized.  The  variously  colored 
woods  of  commerce  always  represent  the  heart- wood  of  the  trees 
from  which  the  wood  has  been  taken,  that  is,  the  inner  annual 
rings,  which  are  usually  very  numerous.  Splint- wood  is  from  the 
younger  tissue,  therefore  from  the  outer  layers.  The  heart- wood  is 
of  a  darker  color  than  that  of  the  splint,  due  to  a  coloring  substance 
deposited  in  the  cell- wall.  Besides  the  coloring  materials,  tannin 
also  is  found  in  the  cell-walls  of  the  heart- wood.  The  lumina  of  the 
vessels  and  tracheids  are  either  closed  by  a  hardened  gum  ( "  heart- 
gum  "),  more  rarely  by  a  resin,  or  by  cells  (tyloses),  which  latter 
grow  through  the  pores  from  the  immediate  vicinity.  These 
changes  render  the  heart-wood  functionless  as  far  as  the  conduction 
of  water  and  the  storing  of  carbohydrates  is  concerned,  but  it  is  on 
the  other  hand  less  subject  to  decay.  The  latter  property  and 
especially  the  occlusion  of  the  vessels,  makes  such  heart- wood  forma- 
tions especially  important,  because  they  serve  as  a  protective  coat- 
ing not  only  to  the  inner  portions  of  the  stem,  but  also  to  external 
injuries;  for  example,  on  the  cut  or  broken  surfaces  of  stems  and 
branches  there  is  formed  a  resinous  or  gummy  protective  covering ; 
hence  the  name  ' '  protective  gum  "  or  "  wound  gum  ' '  (callus) 
(FRANK). 

I  may  only  mention  the  interesting  c '  overflow ' '  growths  which 
proceed  from  the  cambium  in  the  case  of  injuries.  Literally  speak- 


TISSUES  AND  SIMPLE  ORGANS.  93 

ing,  the  cambium  at  the  margin  of  the  injury  overflows  with  callus- 
parenchyma  cells  and  callus-cortex,  gradually  covering  the  injured 
surface ;  finally  the  callus-tissues  meet  and  the  cambial  layers  again 
form  a  closed  ring. 

The  annual  rings  in  the  cortex  are  not  so  definitely  marked  as 
they  are  in  the  wood-tissue.  But  because  of  the  fact  that  the  second- 
ary cortex  receives  an  additional  layer  from  the  cambium  each  year, 
it  is  not  surprising  that  such  annual  rings  should  appear.  The 
annual  layer  deposited  on  the  outer  surface  of  the  cambium  is, 
however,  usually  very  thin,  as  compared  with  the  layer  deposited 
on  the  inside.  It  often  happens  that  there  are  periodical  deposits 
of  thick-walled  bast-cells  formed.  Observation  shows,  however, 
that  such  layers  do  not  agree  exactly  in  number  with  the  annual 
rings  of  the  wood.  . 

By  way  of  comparison  of  the  mechanical  and  conducting  sys- 
tems in  the  monocotyledonous  and  dicotyledonous  stems,  the  follow- 
ing may  be  added,  though  it  is  in  part  a  repetition : 

Among  monocotyledons  the  mechanical  system  has  its  seat 
either  in  an  independent  simple  or  ribbed  bast-ring,  with  which 
the  conducting  bundle  (mestome)  may  be  more  or  less  intimately 
associated,  or  in  a  ring  or  wreath  of  isolated  bast-bundles,  or  in 
strong  bast-linings  which  accompany  the  conducting  bundles. 

In  the  majority  of  dicotyledonous  stems  the  mechanical  system 
is  found  within  the  cambium-ring  of  the  woody  tissue — ' '  intracam- 
bial  libriform  ring."  Among  dicotyledons,  in  general,  the  me- 
chanical system  with  its  elements  ' '  penetrates ' '  the  mestome,  that 
is,  the  conducting  system. 

Among  dicotyledons  there  are  instructive  instances  in  which  a 
bast-ring  or  a  ring  of  bast-bundles  gives  the  stem  the  required  firm- 
ness during  its  early  life-history.  Later  the  mechanical  support  is 
transferred  to  the  gradually  increasing  woody  cylinder,  while  the 
above-mentioned  bast-complexes  are  gradually  displaced  by  bark- 
formations  (BerberiS)  Lonicera,  Platamis,  Betula,  etc.). 

It  may  be  mentioned  here  that  there  are  monocotyledons  (ex- 
ample, Dracaena)  which  have  a  secondary  growth  in  thickness  by 
means  of  a  ring  of  meristematic  tissue.  In  the  case  of  Draccena 
we  have  to  deal  with  fibrous  tracheids  (similar  to  those  of  conifers), 
which  are  formed  inwardly  and  united  with  the  leptome  in  the 
form  of  bundles. 


94  COMPENDIUM  OF  GENERAL  BOTANY. 

Now  we  have  the  opportunity  to  offer  some  suggestions  in  re- 
gard to  the  so-called 

(f)  "Abnormal  Structure  of  Stems." 

The  term  ' 4  abnormal ' '  is  only  meant  to  signify  that  stems  (and 
ultimately  also  the  roots  of  the  plants  concerned)  of  certain  plants 
as  compared  with  the  stems  of  the  majority  of  species  indigenous  to 
our  northern  hemisphere  have  peculiar  structural  conformations. 
The  complex  woody  cylinder  of  Sapindacece,  the  peculiarly  lobed 
or  fissured  stem  of  Bignoniacece,  belong  here.  From  the  fact  that 
we  are  concerned  with  a  group  of  plants  closely  related  by  certain 
life-processes, — a  biological  group,  so  to  speak, — nearly  all  of  which 
are  climbing  or  twining  plants  representing  various  families,  the 
term  "-abnormal"  is  scarcely  justifiable.  Neither  do  we  consider 
a  climbing  plant  occurring  in  a  group  of  non-climbing  plants  as 
abnormal.  The  following  marks  characterize  the  abnormal  ana- 
tomical structure  :  reduced  diameter  of  the  stem ;  diminution  of  the 
loose  medullary  tissue,  especially  of  the  central  medullary  canal ; 
centripetal  tendency  of  mechanical  elements ;  loculose  structure  of 
the  woody  portion,  due  to  the  presence  of  the  elongated,  frequently 
broad,  medullary  rays,  and  especially  to  a  transfer  of  the  leptome 
to  the  woody  body ;  large  diameter  of  vessels  and  sieve-tubes. 
There  are  reasons  to  suppose  that  the  prevailing  tendency  of  the 
growth  in  length  of  the  plants  under  discussion,  and  the  mechanical 
adaptations  to  resist  torsions  and  pulling  tensions,  are  the  result  of 
their  habits  as  climbers,  though  the  researches  in  regard  to  this  sub- 
ject are  not  conclusive.1  Other  so-called  abnormal  types  are  also 
very  probably  phenomena  of  specific  adaptations ;  for  example,  in 
the  autumn  Begonias  very  frequently  show  the  presence  of  vascular 
bundles  in  the  fundamental  tissue,  etc.  This  subject  requires 
further  study,  although  sufficient  has  been  said  to  indicate  that 
the  term  abnormal  as  applied  to  the  above  instances  has  the  same 
meaning  as  it  would  have  if  applied  to  aerial  roots,  since  they  also 
have  a  special  adaptive  structure.  It  is,  however,  very  evident 
that  aerial  roots  are  strictly  normal  for  the  life-processes  of  the 
plants  concerned. 

1  Concerning  this  subject  there  is  a  study  by  AMBRONN  and  myself  in  Flora, 
1881.  Further  investigations  by  SCHENK,  Beitrage  zur  Anatomic  der  Lianen, 
Jena,  1893.  Also  my  own  publications  in  regard  to  Begoniacece  and  Campanulacece, 
Flora,  1879,  and  Monatsber.  der  Berl.  Akad.,  1881. 


TISSUES  AND  SIMPLE  OBGAN8.  95 

(g)  The  Structure  of  Roots. 

The  noticeable  difference  between  the  internal  structure  of  roots 
and  stems  suggests  the  question :  What  are  the  physiological  causes 
which  produce  such  a  difference  ?  Only  since  SCHWENDENER'S 
physiological  studies  of  tissues  have  we  been  enabled  to  give  an 
approximately  correct  answer  to  this  question.  According  to  the 
requirements  of  mechanical  tension,  we  find  a  central  arrangement 
of  the  relatively  firm  elements  (see  discussion  of  mechanical  tis- 
sues). This  centripetal  tendency  of  mechanical  elements  governs 
the  arrangement  of  tissues  in  the  root ;  the  absence  of  a  medullary 
tissue,  or  at  least  the  reduction  of  the  same  to  a  minimum,  is 
thereby  readily  explained  (teleologically,  not  causal-mechanically). 


FIG.  57. — Cross-section  of  the  root  (diagramatic). 

*,  Bundle-sheath  ;  p,  pericambium.    The  root  is  "  tetrarch"  ;  between  the  four  vascular  bun- 
dles and  the  four  groups  of  sieve-tissue  lie  the  wood-parenchyma  and  the  mechanical  cells. 

The  fact  must  not  be  overlooked  that  the  older  and  more  centrally 
located  root-portions  serve  primarily  for  the  conduction  of  water, 
while  the  root-tip  portions  are  specially  qualified  to  take  food  sub- 
stances from  the  soil.  This  predominating  conducting  function  of 
older  root-portions  requires  anatomical  adaptations  which  are  most 
suitably  met  by  the  compact,  narrowed,  central  vascular  bundle. 
It  is  known  that  the  primary  cortex  very  often  loses  its  leaves,  in 
which  case  there  is  in  reality  only  a  central  bundle  remaining. 
Leaving  the  root-cap  out  of  consideration  for  the  present,  there  are 
three  anatomical  differences  between  the  root  and  the  stem.  These 
differences  are  as  follows. 


96  COMPENDIUM  OF  GENERAL  BOTANY. 

1.  The  central  arrangement  of  the  conducting  elements  and 
the  mechanical  elements  in  the  root;    their  more  peripheral  ar- 
rangement in  the  stem. 

2.  The  centripetal  development  of  primordial  vessels  in  the 
root ;  their  centrifugal  development  in  the  stem. 

3.  The  tangential  arrangement  of  the  two  conducting  bundle- 
portions,  that  is,  the  leptome  and  the  hadrome  (sieve-portion  and 
vessel-portion),  in  the  root ;  their  radial  arrangement  in  the  stem. 


FIG.  58. 

A,  Diagramatic  ;  B,  anatomical  representation  of  the  segment  x.    (After  Haberlandt.) 

Ad  2.  This  anatomical  characteristic  is  perhaps  closely  related 
to  the  first,  in  that  its  purpose  seems  to  be  to  utilize  the  cen- 
tral space  as  much  as  possible.  This  arrangement  is  also  ad- 
vantageous in  that  it  brings  the  vessels  nearer  the  root-hairs  which 
absorb  the  moisture  from  the  soil.  The  vessels  first  formed  (pri- 


TISSUES  AND  SIMPLE  ORGANS.  97 

maiy  vessels)  are  somewhat  scattered  through  the  root,  as  seen  in 
cross-section. 

Ad  2  and  3.  The  number  of  vascular  bundle-groups  (hadrome- 
bundles)  corresponds  to  the  number  of  leptome-bundles,  and  ac- 
cording to  this  numerical  relation  roots  are  designated  as  ' '  di- 
arch,"  "triarch,"  "tetrarch,"  etc.,  "  polyarch."  The  latter, 
that  is,  many  bundle-groups,  occur  most  frequently  among  mono- 
cotyledons ;  the  former  ("  diarch, "  "  triarch, ' '  etc.)  are  more  com- 
mon among  dicotyledons.  This  anatomical  relation  is  perhaps  the 
reason  why  secondary  growth  in  thickness  cannot  take  place  in  the 
roots  of  monocotyledons,  since  the  numerous  primordial  bundles  re- 
quire eo  ipso  a  maximum  circumference  for  their  maturation. 
Among  dicotyledonous  roots  secondary  growth  in  thickness  oc- 
curs frequently.  As  is  well  known,  conifers  and  other  trees  often 
have  roots  a  foot  or  more  in  diameter. 

How  do  such  roots  grow  in  thickness  ?  Fig.  58  represents 
the  period  at  which  secondary  growth  in  thickness  begins.  The 
meaning  of  the  letters  are  clear,  with  the  exception  of  -y,  which  in- 
dicates the  cambial  tissue.  Tangential  walls  are  formed  within 
the  sieve- tube  bundles;  cell- divisions  continue  along  the  sides  of 
the  bundles ;  finally,  this  process  also  begins  immediately  outside  of 
the  primordial  vessels,  upon  which  the  cambial  ring  is  completely 
closed.  During  the  earlier  stages  this  ring  is  two,  three,  or  more 
lobed  or  loculose ;  later,  when  the  secondary  wood-formation  has 
begun  within  the  primordial  albumen-bearing  tissue,  it  becomes 
circular.  In  general,  this  cambium  behaves  like  that  of  the  stem, 
forming  woody  elements  (wood-parenchyma,  medullary  rays,  vessels 
and  tracheids)  inwardly,  leptome  and  ultimately  mechanical  bast-cells 
outwardly.  Thus,  finally,  the  root  can  only  be  distinguished  from 
the  stem  by  the  structure  of  the  organic  centre ;  in  the  root  this 
must  show  a  central  tissue  of  three  or  more  radiating  primordial  ves- 
sels instead  of  the  medulla.  Later  the  primordial  leptome  of  the 
numerous  conducting  bundles  is  no  longer  found  in  the  centre ;  it 
is  crowded  toward  the  periphery  by  the  formation  of  the  woody 
tissue.  According  to  the  above,  there  are  certain  portions  of  the 
pericambium  p  which  take  part  in  the  formation  of  the  cambium- 
ring,  namely,  those  cells  which  lie  above  the  vessels  first  formed. 
The  bundle-sheath  s  (protective  sheath)  must  either  grow  with  the 
increase  in  thickness  of  the  bundle  or  rupture.  Such  growth  in 


98  COMPENDIUM  OF  GENERAL  BOTANY. 

the  bundle-sheath  has  actually  been  observed.  Should  the  central 
portion  be  wanting,  it  would  be  difficult  to  decide  definitely  whether 
the  given  wood  belonged  to  a  root  or  to  a  stem  (a  difficulty  encoun- 
tered by  palaeontologists). 

Fleshy  roots *  (turnips)  owe  their  condition,  as  a  rule,  either  to 
the  prevalence  of  the  parenchyma  (longitudinal  parenchyma  and 
ray-parenchyma)  in  the  woody  body  or  to  the  extensive  develop- 
ment of  the  secondary  cortex. 

"  Abnormal"  root-structure  is  to  be  considered  from  a  stand- 
point analogous  to  that  of  the  stems  referred  to  above. 

(K)  Anatomy  of  the  Transition-zone  between  the  Stem  and 

the  Hoot. 

The  question  as  to  how  the  existing  differences  between  the 
root  and  the  stem  become  equalized  at  the  transition-zone  must 
force  itself  upon  every  anatomist  who  has  studied  the  stem  and 
root.  Evidently  the  elements  which  conduct  water  in  the  roots 
continue  the  same  function  in  the  stem;  hence  it  must  undergo  its 
typical  transformation  into  stem-structure  at  a  region  near  the  sur- 
face of  the  soil.  The  description  given  by  DE  BARY'  (after 
STRASBRUGER)  of  the  case  of  Biota  orientalis  is  simple  and  explicit. 
The  student  can  easily  study  the  transition-zone  in  longitudinal  and 
cross  sections. 

The  hypocotyledonous  stem  contains  two  bundles  in  its  upper 
part,  which  extend  perpendicularly  downward  from 
the  two  cotyledons ;  the  bundle  of  the  main  root  is 
diametrically  diarch.    In  each  of  the  two  cotyledonous 
bundles  the  phloem  (leptome)  divides  into  two  equal 
parts  near  the  base  of  the  cotyledons.     The  leptome- 
halves  diverge  more  and  more,  and  are  finally  in  the 
same  tangential  plane  with  the  hadrome-group.     Each 
one  of  the  sieve-tube  groups  approaches  a  correspond- 
FIG.  59.        .ng  group  from  the  Other  bundle  and  unites  with  it 
to  form  a  broad  leptome-group.     The  elements  of  both  portions 
of  the  vascular  system  (leptome  and  hadrome)  undergo  a  similar 
displacement  or  torsion  at  the  same  level  of  their  course ;   so  that 

1  WEISS,  J.  E.,  Flora,  1880  ;  also  other  authors. 

2  Comp.  Anatomy,  page  386.     Also  DODEL,  Pringsheim's  Jahrbticher,  VIII. 


TISSUES  AND  SIMPLE  ORGANS.  99 

the  innermost  (primitive)  vessels  incline  most  strongly  toward  the 
outside,  the  next  following  less  strongly,  etc.  The  accompanying 
figure  (59)  represents  the  latter  displacement  for  the  left  side. 

A  certain  regularity  also  exists  in  the  union  of  the  bundle-ele- 
ments of  root-branches  with  the  corresponding  elements  of  the 
main  root.  Without  entering  into  the  particulars  of  these  and 
similar  structural  relations,  we  will  direct  attention  to  the  fact  that, 
in  the  majority  of  cases,  the  outer  angle  of  a  vascular  plate  of 
the  main  root  is  that  to  which  the  secondary  vascular  system 
becomes  united.  The  vessels  of  both  roots  unite ;  the  leptome- 
groups  are  derived  from  the  immediate  vicirity. 

(i)  The  Special  Physiology  of  the  Movements  of  Food-substances 
and  Water  in  Plants. 

The  paths  in  which,  and  the  forces  through  which,  water  and 
food-substances  are  moved  will  next  claim  our  attention. 

Movement  of  the  above-mentioned  substances  must  take  place. 
Carbohydrates,  especially  starch,  must  be  transported  from  the 
places  of  formation  to  the  centres  of  nutrition,  and  eventually  to 
the  storing  tissues;  and  again  from  the  latter  to  the  centres  of 
nutrition :  or,  in  other  words,  from  the  green  assimilating  organs 
to  the  tubes  and  stems,  to  developing  roots,  flowers,  seeds,  etc., 
and  from  tubes  and  other  storage- tissues  to  the  places  of  organ- 
formations,  such  as  the  root-tip,  the  apical  area  of  the  stem,  etc. 
Farther,  the  organs  of  great  surface-expansion  (leaves)  require  a 
large  quantity  of  water,  for  purely  physical  reasons  (on  account  of 
evaporation),  which  must  be  conducted  upward  from  the  roots. 

«.   Conduction  of  Albumen. 

Investigations  concerning  the  seat  of  albumen-formation  (FRANK, 
SCHIMPER)  have  perhaps  already  proceeded  so  far  as  to  show  that 
every  living  cell  (not  only  the  green  ones)  which  contains  nitrates 
and  a  corresponding  C-bearing  substance  may  be  considered  as  a 
centre  of  amide-formation,  and  secondarily  also  of  albumen. 
(Plasm  is  an  essentially  albuminous  substance.)  We,  however, 
at  once  meet  with  difficulties  in  trying  to  explain  the  circulation  of 
albuminous  substances.  Some  uncertainty  has  recently  arisen  as 
to  whether  the  sieve-tube  tissue  should  be  considered  as  albumen- 


100  COMPENDIUM  OF  GENERAL  BOTANY. 

conducting  or  as  albumen-storing  (FRANK).  From  the  anatomical 
structure  of  sieve-tubes  we  may,  however,  safely  assume  that  they 
are  qualified  to  permit  the  mass  movement  of  undissolved  albumin- 
oid substances  (see  above).  The  old  and  well-known  girdling  ex- 
periments teach  that  the  substances  necessary  in  the  formation  of 
organs,  that  is,  albumen  and  carbohydrates,  are  checked  in  their 
course  when  the  entire  bark  is  removed.  The  question  whether 
the  two  plastic  substances  each  require  a  special  path,  that  is,  pri- 
mary cortex  for  the  one  and  secondary  cortex  (leptome)  for  the 
other,  or  whether  the  conditions  are  otherwise,  is  still  unsettled. 
FRANK  is  inclined  to  assume  that  the  primary  and  secondary 
cortex,  without  the  sieve-tubes,  is  chiefly  employed  in  the  conduc- 
tion of  carbohydrates  and  amides  (the  latter  are  considered  as  cir- 
culatory forms  of  albumen).  The  opinion  that  the  contents  of  the 
sieve-tubes  (especially  albumen)  are  essentially  serviceable  in  the 
cambium  for  the  formation  of  tissues  is  doubtless  correct,  but  it 
seems  in  exact  opposition  to  the  principles  of  physiological  anatomy 
to  assume  that  the  elongated  elements  of  the  sieve-tubes  simply 
serve  the  function  of  a  storage -tissue  in  which  albumen  remains  at 
rest  until  required  for  use  in  the  immediate  vicinity.  FRANK'S 
process  of  reasoning  will  no  doubt  bring  us  nearer  the  truth.  Ac- 
cording to  this  authority,  the  soluble  amides  and  the  carbohydrates 
circulate  in  the  parenchyma.  From  the  amides  are  formed  mu- 
cous (undissolved)  albuminous  substances ;  in  the  winter  these  col- 
lect in  the  sieve-tabes  and  remain  at  rest.  At  the  time  of  cambial 
activity  this  mucous  mass  in  the  sieve-tube  system  oscillates,  due  to 
the  bendings  of  the  stem  and  changes  of  the  turgor-force  accompa- 
nied by  a  gradual  reabsorption  of  the  albumen.  Frank's  studies 
(and  those  of  his  pupils)  may  perhaps  soon  lead  to  the  recognition 
of  the  fact  that  the  sieve-tubes  really  form  a  storage  system,  but  that 
they  are  also  admirably  adapted  to  permit  mass-movement  in  a  longi- 
tudinal direction  during  active  assimilation. 

Since  we  have  referred  to  u  girdling,"  we  may  also  mention 
the  well-known  experiment  which  is  made  as  follows :  aleaf -bear- 
ing twig  (of  willow)  is  girdled  a  little  above  its  leafless,  lower  end 
and  the  cut  end  placed  into  moist  earth  up  to  a  point  somewhat 
above  the  girdle.  No  roots,  or  but  very  few,  appear  below  the 
girdle,  while  numerous  roots  and  callus  are  formed  above  it.  A 
current  of  formative  substances  passes  from  the  assimilating  leaves. 


TISSUES  AND  SIMPLE  ORGANS.  101 

downward    along  the  cortex;   wherever  the  path  is  broken,   this 
substance  is  at  once  converted  into  callous  tissue. 

The  movement  of  undissolved  albuminous  substances  in  the 
sieve-tubes,  like  that  of  the  milk-sap  mentioned  above,  is  a  mass- 
movement.  The  causes  for  this  movement,  though  not  definitely 
determined,  have  already  been  referred  to.  Gravity,  outer  me- 
chanical pressure  upon  the  soft  elements,  and  turgor- oscillations 
in  the  neighboring  tissues  no  doubt  assist  in  bringing  about  this 
movement. 

/3.  Conduction  of  Carbohydrates. 

Here,  and  in  general  with  substances  in  solution  which  must 
pass  through  plasmic  membranes  and  cell-membranes,  we  are  con- 
cerned with  molecular  movements,  which  belong  to  the  domain  of 
osmosis.  General  statements  only  will  be  made  now ;  particulars 
will  be  given  below. 

The  physical  considerations  of  osmotic  action  differentiate  (1) 
hydro-diffusion,  the  osmotic  interchange  of  two  miscible  substances 
without  any  separating  membrane ;  from  (2)  diosmosis  in  the  usual 
sense,  that  is,  a  process  similar  to  (1)  with  a  dyalizing  membrane 
or  porous  substance.  Both  processes  occur  in  the  vegetable  cell. 

Ad  1.  In  an  assimilating  palisade- cell  exposed  to  the  sunlight 
several  currents  must  be  formed  in  obedience  to  the  principle  that 
the  current  is  formed  at  right  angles  to  the  lines  of 
equal  concentration  (see  Fig.  60).  It  is  assumed 
that  the  maximum  concentration  of  sugar,  for  ex- 
ample, is  at  5  (Fig.  60).  The  sugar-molecules  will 
then  move  in  the  direction  of  the  arrows ;  the  wrater- 
molecules  in  the  opposite  direction.  "Wherever  a 
crystal  or  a  starch-grain  grows  within  a  cell,  there 
are  produced  such  zones  of  concentration  in  the 
surrounding  liquid,  and  the  respective  movements 
will  take  place.  FlG-  60- 

(Modified       from 

Ad  2.  If  the  solutions  in  neighboring  cells  are  of  Haberiandt.) 
unequal  concentration,  a  new  complication  arises,  which  leads  us 
into  a  branch  of  physiology,  in  part,  yet  unexplained.  The  more 
recent  investigators  (BKUCKE,  PFEFFER)  have,  however,  given  many 
explanations  and  suggestions.  Whatever  applies  to  processes  that 
may  be  traced  to  living  protoplasm  is  also  applicable  here ;  the 


V 

/ 
*' 

\i 
\\3 


102  COMPENDIUM  OF  GENERAL  BOTANY. 

behavior  of  the  living  primordial  utricle  in  the  movement  of  food- 
substances  from  cell  to  cell  is  not  well  understood.  It  is,  however, 
very  clear  that  a  living  cell  in  contact  with  water  will  increase  its 
hydrostatic  pressure  by  taking  in  more  water. 

The  so-called  transitory  starch  which  occurs  in  the  form  of 
small  granules  within  the  cells  in  which  starch  circulates  is  of 
special  importance  in  the  circulation  of  soluble  starch.  We  can 
somewhat  understand  the  function  of  this  transitory  starch  when  we 
learn  that  the  precipitation  of  starch-substance  in  the  form  of  solid 
granules  produces  a  decrease  in  the  degree  of  concentration  in  the 
surrounding  starch  solution.  As  a  result  new  currents  are  set  in 
motion  toward  the  granules ;  but  why  these  granules  are  formed  at 
the  suitable  moment,  and  why  they  are  again  dissolved  in  order 
that  the  current  may  continue  in  the  same  direction  and  thus  make 
way  for  new  incoming  currents  and  new  precipitates  of  starch-sub- 
stance, is  but  little  understood.  The  processes  of  hydro-diffusion 
and  diosmosis  are,  of  course,  frequently  combined  in  the  circulation 
of  food-substances.  According  to  SACHS',  we  may,  in  general, 
express  ourselves  as  follows :  Every  growing  part  of  a  plant  acts  as 
a  centre  of  attraction  for  the  available  food-substances;  every 
storage-tissue  or  receptacle  and  every  assimilating  organ  acts  as  a 
centre  of  repulsion  as  compared  with  the  growing  portion. 

Many  of  the  earlier  and  also  of  the  more  recent  physiological 
and  anatomical  investigations,  especially  those  of  SACHS,  also  those 
of  HABERLANDT  and  of  SCHIMPER,  throw  light  upon  the  conveyance 
of  assimilates  from  the  leaves.  We  are  here  concerned  principally 
with  the  adaptive  arrangement  of  the  assimilating  cells  and  other 
leaf- tissues  with  regard  to  the  vascular  system  and  the  mode  of  con- 
duction within  the  tissues  named  (see  Physiological  Anatomy  of  the 
Assimilating  System,  Function  VI).  In  the  early  sixties  SACHS  had 
already  observed  that  germinating  plants  free  from  starch  (etiolated) 
when  brought  into  the  sunlight  would  soon  contain  small  starch- 
grains,  first  in  the  chlorophyll-grains  of  the  leaf,  then  also  in  the 
conducting  tissues  of  the  petioles  and  internodes;  these  starch- 
granules  would  disappear  when  the  plant  was  placed  in  the  dark 
and  again  reappear  when  brought  into  the  light.  As  a  result  of 
these  investigations  by  SACHS,  and  also  those  of  more  recent  authors, 


Vorlesungen,  page  439. 


TISSUES  AND  SIMPLE  ORGANS.  103 

we  shall  here  emphasize  the  fact  that  the  following  tissues  are 
especially  adapted  to  conduct  starch  and  other  food-substances 
which  are  free  from  nitrogen :  the  vascular  bundle-sheath  of  the 
leaf -blade  and  the  parenchyma  immediately  about  the  larger  bundles, 
the  parenchyma  of  the  petioles  and  stern-organs,  inclusive  of  the 
wood-parenchyma  and  the  medullary  rays.  The  l '  path  ' '  broadens 
continually,  similar  to  the  path  of  blood -circulation  in  man. 

y.   Conduction  of  Water. 

The  history  of  our  science  has  undergone  great  oscillations  in 
regard  to  the  movements  of  water  in  the  plant-body.  By  c '  water  ' ' 
we  mean  the  liquids  which,  as  is  known,  always  contain  mineral 
salts  and  other  substances  in  solution,  and  which  are  taken  from 
the  soil  by  the  roots. 

It  is  generally  agreed  that  the  current  of  water  passes  upward 
in  the  woody  tissue  of  dicotyledons  and  conifers,  especially  in  the 
younger  annual  rings  (splint-wood).  Let  us  further  consider  cir- 
culation in  dicotyledons  and  conifers. 

In  agreement  with  many  authors,  I  find  it  impossible  to  accept 
SACHS'  theory  of  ' '  imbibition. ' '  The  future  history  of  botany 
will  no  doubt  show  that  it  was  the  reputation  of  the  originator  of 
this  hypothesis  that  made  its  acceptance  possible  for  so  long  a  time. 
According  to  this  hypothesis,  we  are  to  assume  the  following: 
water  does  not  pass  through  the ,  cell-cavities  (lumina),  but  through 
the  cell- wall  substance.  The  living  woody  cell- wall  contains  water 
obtained  by  imbibition,  and  so  long  as  the  cell-wall  is  not  dry  this 
water  which  has  been  imbibed  is  very  readily  displaced.  Unligni- 
fied  (not  woody)  cell- walls  and  woody  cell- walls  which  have  once 
become  dried  do  not  possess  this  property.  Sachs  further  empha- 
sizes the  fact  that  the  force  with  which  water  is  retained  in  the  cells 
which  are  capable  of  imbibition  is  so  great  that  it  makes  no  dif- 
ference whether  the  imbibing  cell- body  lies  ten  or  one  hundred 
metres  above  the  water-absorbing  roots,  just  as  in  the  case  of  the 
saline  ocean-water  it  makes  no  difference  whether  the  salt-molecule 
in  solution  floats  one  hundred  or  one  thousand  metres  above  the 
bottom  of  the  ocean."  If  from  such  a  system  of  water- soaked 
cells  water  is  removed  at  one  end  by  evaporation  (in  the  leaves), 

1  Vorlesungen,  page  290. 


104  COMPENDIUM  OF  GENERAL  BOTANY. 

there  is  a  retrogressive  movement  of  water-molecules  induced  by 
this  disturbance  which  continues  to  the  root  and  which  tends  to 
re-establish  the  ' '  state  of  saturation. ' ' 

Critics  rightly  observe  that  the  great  force  with  which  the 
water  obtained  by  imbibition  is  held  by  the  molecules  of  the  cell- 
wall  requires  a  correspondingly  great  force  to  separate  it  from  the 
molecules  of  the  cell- wall  and  to  guide  it  onward ;  in  other  words, 
the  force  of  friction  must  be  very  great.  From  Schwendener's l 
explanations  it  is  implied  that  the  movement  of  water  in  an  imbib- 
ing system  is  subject  to  the  same  law  as  the  movement  of  water  in 
a  capillary  system ;  that  therefore  the  moving  force  becomes  very 
great  as  the  diameter  of  the  tubes  becomes  immeasurably  small. 
Schwendener  also  discusses  the  differences  between  capillarity  and 
imbibition  as  emphasized  by  Sachs.  From  this  discussion  we  select 
the  following :  Entrance  of  water  into  a  solid  body  in  the  state  of 
aggregation  may  take  place  whether  the  volume  of  the  body  re- 
mains the  same  or  whether  it  becomes  smaller  or  larger ;  in  this 
respect  capillarity  and  imbibition  are  alike.  If  we  suppose  a  series 
of  glass  plates  to  be  superimposed  upon  each  other,  the  height  of 
this  pillar  may  be  increased  if  the  edges  are  brought  in  contact 
with  water,  provided  the  spaces  between  the  plates  are  not  too 
great.  If  the  intervening  spaces  are  increased  above  a  certain 
limit,  the  height  of  the  pillar  is  reduced  by  capillary  action. 
Therefore  we  cannot  correctly  say  that  when  the  spaces  of  a 
body  into  which  water  enters  are  pre-formed,  and  when  the  limit- 
ing walls  of  these  spaces  are  firm  and  immovable,  friction  is  great ; 
and  if  such  spaces  are  not  previously  formed,  but  are  produced  by 
the  water  itself,  whereby  the  volume  is  increased,  friction  is  re- 
duced to  a  mimimum  or  zero.  There  is  nothing  characteristic  of 
capillarity  in  the  immobility  of  the  walls  of  a  system,  therefore 
nothing  essentially  different  from  imbibition  accompanied  with  in- 
crease in  volume.  The  term  ' c  imbibition ' '  is,  however,  not 
superfluous,  or  synonymous  with  capillarity.  We  say  a  starch- 
grain  is  imbibed  when  it  has  become  saturated  with  water  (from 
internal  causes  due  to  processes  of  growth  (COBRENS)  without  chang- 
ing its  structure.  This  condition  is  strictly  different  from  that  of 
swelling,  in  which  water  is  also  taken  up  (usually  a  greater  or  smaller 


1  Untersuchungen  liber  das  Saftsteigen:    Sitz.-Ber.  der  Berl.  Akad.,  1886. 


TISSUES  AND  SIMPLE  ORGANS.  105 

quantity  than  in  imbibition,  hence  an  irregular  quantity),  but  from 
external  causes,  and  always  with  the  result  that  the  structure  of  the 
grain  is  permanently  changed.  Imbibed  membranes,  as  well  as 
starch-grains  after  drying,  can  take  up  a  definite  amount  of  water 
and  assume  their  original  volume ;  swollen,  similarly  treated  cell- 
walls  and  starch-grains  will  not  assume  their  original  volume  (CoR- 
RENS).  Imbibition  is  therefore  something  specific,  a  taking-up  of 
water  without  change  in  structure,  a  change  which  can  not  be 
equally  well  designated  by  the  term  c  4  capillary  action. ' ' 

The  ready  displacement  of  water  in  membranes,  mentioned  by 
SACHS,1  and  the  great  frictional  resistance  which  must  exist  accord- 
ing to  physical  laws,  are  in  direct  opposition.  Moreover,  the  above- 
mentioned  displacement  has  not  been  demonstrated  by  unimpeach- 
able experiments.  Imbibed  membranes,  for  example  of  Lami- 
naria,  show  this  high  frictional  resistance  according  to  the  investi- 
gations of  SACHS.  The  hypothesis  of  Sachs  had  its  origin  at  a  time 
when  the  anatomical-physiological  conception,  which  later  brought 
about  such  excellent  results,  was  but  little  understood.  At  that 
time  the  best  workers  in  our  branch  of  science  treated  the  cell-forms 
of  the  plant-body  according  to  a  strictly  anatomical  method  based 
upon  the  evolutionary  history  of  development  so  characteristic  of 
^AGELI  and  his  school.  The  conclusions  of  Nageli  and  Schwen- 
dener's  2  critical  speculative  studies  concerning  this  subject  point 
to  wholly  different  results  and  do  not  formulate  a  concluded  theory. 
Although  these  studies  preceded  the  advance  made  in  our  knowl- 
edge concerning  endosmosis,  through  the  investigations  of  Pfeft'er 
(1877)  the  conclusions  of  Nageli  still  hold  good.  They  are  as  fol- 
lows :  "It  only  remains  for  us  to  distribute  the  water-moving 
forces  among  certain  numerous  points.  Since  there  is  no  reason 
why  we  should  concentrate  them  in  definite  cells  of  the  tissues,  it 
seems  most  natural  to  locate  them  in  each  and  every  cell  containing 
cell-sap.  Only  when  the  energies  of  the  tree  are  equally  dis- 
tributed in  all  cells  are  such  diminished  tensions,  as  occur  in  the 
plant,  explainable."  SCHWENDENER'S  3  more  recent  investigations 
verify  his  former  conclusions  as  well  as  those  of  Nageli.  Based 
upon  these  two  works  (1877  and  1886),  and  also  upon  Pfeffer's 

1  Porositat  des  Holzes:  Arbeiten  des  Bot.  Inst.  in  Wurzburg  II,  1879. 

2  Das  Mikroskop,  1877. 

3  Sitz.-Ber.  der  Berliner  Akademie,  1886. 


106  COMPENDIUM  OF  GENERAL  B01ANY. 

experiments  concerning  osmosis,  I  shall  offer  the  following  explan- 
atory statements : 

1.  Capillarity  cannot  replace  the  molecules  of  water  removed 
by  evaporation  from  the  periphery  of  a  tree.    In  a  capillary  system 
one  meter  in  height  in  which  the  possible  height  of  the  column  of 
water  is  fifty  meters,  according  to  the  diameter  of  the  interstices, 
sinking  due  to  evaporation  from  a  large  area  is  more  rapid  than 
the  rise  due  to  capillarity.     The  latter  force  is  therefore  without 
effect    for    greater    heights.     This    experiment    by    Nageli    and 
Schweiidener  was  made  with  a  cylinder  of  starch-paste  in  a  long 
glass  tube. 

The  fact  that  the  capillary  attraction  of  the  interior  of  the  cell- 
wall  would  in  itself  be  sufficient  to  raise  the  water-column  at  least 
one  hundred  feet  is  not  of  decisive  moment,  since  in  a  unit  of  time 
the  sinking  of  the  column  due  to  evaporation  is  much  more  rapid 
than  the  rising. 

2.  With  reference  to  water-movements,  imbibition  of  the  cell- 
wall  is  only  a  special  case  of  capillary  action.     In  both  there  is 
friction  of  water- molecules  upon  each  other,  there  is  in  both  a  solid 
framework  within  which  water  moves  or  circulates ;   firmness  and 
immobility  of  the  enclosing  walls  are,  however,  not  essential  prop- 
erties of  a  capillary  system.     (Compare  the  above  with  the  state- 
ments of  SACHS.) 

3.  The  osmotic  forces  of  the  living  cells  come  into  play.     Here 
we  must  make  a  distinction  between  that  which  osmotic  forces  can 
accomplish  and  that  which  they  can  not  accomplish  within  the  liv- 
ing woody  cells,  of  course  only  in  so  far  as  our  knowledge  will 
permit  us  to  see  and  comprehend.     Turgescent    living    cells   no 
doubt,  under  certain  conditions,  will  force  water  into  neighboring 
dead  elements  (vessels  and  tracheids)  in  the  same  way  as  they  would 
force  water  into  a  vertical   glass   tube  (demonstrated  by  experi- 
ments). 

A  high  hydrostatic  pressure  within  a  living  cell  is  produced  as 
follows.  The  water-attracting  force  of  the  substances  in  solution  in 
the  cell-sap  (nitrates,  sugar,  etc.)  draws  the  water  which  is  found 
in  the  vicinity  of  the  cell  through  the  cell- wall  and  primordial  utri- 
cle into  the  cell-lumen.  The  interstices  in  the  living  primordial 
utricle  are  presumably  very  minute.  As  has  been  demonstrated, 
the  molecules  of  sugar  in  solution  in  the  cell-sap  require  many 


TISSUES  AND  SIMPLE  ORGANS.  10T 

hours  before  they  will  diffuse  into  the  surrounding  water.  There- 
fore either  the  molecules  of  sugar  cannot  pass  through  the  primor- 
dial utricle,  or  more  molecules  of  water  pass  inward  than  sugar-  and 
salt-molecules  pass  out.  The  latter  phenomenon  makes  it  evident 
that  such  a  plasmic  interstice  has  a  certain  depth  and  width,  but 
that  water  takes  a  position  at  the  periphery  of  the  same  and  passes 
into  the  cell  because  of  the  greater  affinity  of  the  saline  substance 
to  the  water.  In  the  middle  of  the  interstitial  canal  the  salt-  and 
water -molecules  move  in  an  equalized  or  balanced  relationship 
(hydro-diffusion),  while  in  the  immediate  vicinity  of  the  cell-wTall 
substance  there  is  an  excess  of  water  flowing  inward.  Hence  it 
matters  not  whether  none  or  a  few  sugar-  or  salt-molecules  pass 
outward :  water  will  accumulate  in  the  interior  of  the  cell ;  the 
hydrostatic  pressure  of  the  cell  increases;  the  cell-membrane, 
which  forms  the  support  of  the  primordial  utricle,  becomes  more 
and  more  tense  and  in  return  it  exerts  an  equal  pressure,  due  to  its 
elasticity,  upon  the  cell-contents.  It  is  only  necessary  to  assume 
that  at  certain  points — doubtless  the  thin  areas  of  the  cell-wall,  the 
pores — the  primordial  utricle  is  more  readily  permeable  to  water 
than  at  other  points.  If  these  cells  lie  in  contact  with  vessels,  then 
the  thin  areas  are  comparable  to  openings  at  which  suction-tubes  are 
placed.  If  the  endosmosis  of  water  in  living  cells  lying  near  a  vas- 
cular system  continues,  the  infiltration  into  the  vessels  will  also 
continue,  and  the  question  arises,  How  high  can  the  column  of  water 
be  raised?  This  height  is  evidently  dependent  upon  the  nature  of 
the  primordial  utricle,  on  the  composition  of  the  endosmotically 
acting  substances,  on  the  relative  concentration  and  temperature  of 
the  liquids,  and  on  the  diameter  of  the  vessels.  Potassium  nitrate, 
for  example,  possesses  a  very  high  "  endosmotic  equivalent,"  as 
has  been  demonstrated  by  PFEFFER.  His  experiments  were  made 
with  clay-cells,  the  interior  of  which  were  lined  with  a  film  of 
cupric  ferrocyanide.  For  a  one  per  cent  potassium  nitrate  solution 
the  pressure  was  sufficient  to  cause  the  mercury-column  to  rise  175.8 
cm. 

If  one  supposes  the  forcing  in  of  water  to  be  interrupted,  so 
that  water  and  air  pass  into  the  vessel  alternately,  there  is  produced 
the  so-called  c  4  chain  of  Jamin. ' ' 

Bleeding  (Blutungsdruck) — a  better  term  than  ' '  root-pressure, ' ' 
because  we  are  not  concerned  with  any  specific  activity  of  the  roots 


108  COMPENDIUM   OF  GENERAL  BOTANY. 

— is  the  term  applied  to  the  above- explained  process.  This  phe- 
nomenon is  referable  to  living  cells  in  general  (experiments  with 
various  stems  by  PITRA  and  C.  KRAUS).  Pressure  due  to  bleeding 
sinks  very  materially  during  the  vegetative  period.  A  safe 
maximum  of  this  pressure  (observed  in  a  grape-vine  during  the 
spring)  may  be  represented  by  a  column  of  mercury  about  100 
cm.  high  (HALES).  However,  as  already  stated,  the  positive  pres- 
sure is,  in  general,  very  materially  reduced  during  the  period 
of  maximum  transpiration.  If,  therefore,  the  highest  positive 
pressure  observed  can  raise  a  column  of  water  to  only  15  m.,  or 
usually  less — say  2  m. — we  cannot  rationally  explain  the  rise  of 
the  sap  by  supposing  the  propelling  force  to  be  at  the  base  of  the 
stem  (in  the  root-system)  forcing  the  water  upward  several  hundred 
feet  after  the  manner  of  a  force-pump.  This,  however,  does  not 
exclude  the  possibility  that  osmotic  forces  of  lesser  intensity  may 
occur  at  various  heights  in  a  tree  and  come  into  active  play  in 
the  living  cells  in  the  neighborhood  of  vessels  and  tracheids; 
in  fact,  this  has  been  proven  in  a  number  of  instances.  This 
carries  us  back  to  the  ideas  of  Nageli  and  Schwendener  expressed 
above. 

We  must  also  mention  the  phenomenon  of  water -excretion, 
observed  in  various  herbaceous  plants  by  different  authors.1  At 
night  during  the  spring  when  the  bleeding-pressure  is  high  and 
transpiration  low  there  are  noticeable  copious  excretions  of  water  at 
certain  areas — for  example,  from  the  apices  of  monocotyledonous 
leaves  as  well  as  from  the  serrate  edges  and  apices  of  dicotyledo- 
nous leaves.  Frequently  there  exists  a  special  secreting  apparatus 
placed  at  given  points.  The  water-conducting  vessels  expand  fan- 
like  or  brushlike  at  the  points  referred  to ;  above  the  vascular 
ends  there  is  sometimes  a  special  tissue  of  colorless  cells,  the 
4 '  epithein. ' '  Structures  resembling  stomata  (the  ' '  water-pores  ' ') 
are  found  grouped  at  certain  epidermal  areas :  they  facilitate  the 
escape  of  water. 

The  above-cited  investigations  by  SCHWENDENER  concerning  the 
ascent  of  sap  (1886)  give  further  evidence  of  progress  toward  the 
solution  of  the  problem  under  consideration,  although  we  are  far 


1  SACHS,  Experimental  Physiologic  (1865),  p.  236.     Also  more  recently  VOL- 
KENS,  tJber  Wasserausscheidung,  etc.,  Dissertation,  Berlin,  1882. 


TISSUES  AND  SIMPLE  ORGANS. 


109 


1 

1 

L 

11 

r        i 

1 

.1      , 

from  a  satisfactory  explanation.  Among  others  the  author  1  has. 
carried  on  some  special  investigations  in  regard  to  this  problem.  I 
wish  to  state  in  advance  that  Schwendener  for  a  time  withheld 
judgment  in  regard  to  my  conclusions, 
but  that  he  defended  some  of  my  pro- 
positions against  attacks.  Therefore 
before  entering  more  particularly  into 
Schwendener 's  important  investigations 
I  will  here  introduce  my  explanation. 

According  to  my  interpretation,  there 
are  two  forces  employed  in  the  ascent  of 
the  cell-sap:  1 ,  endosmosis ;  2,  capillarity 
— the  former  a  moving  force,  the  latter 
a  holding  or  retaining  force.  Two  forms 
of  elements  represent  the  path  in  which 
cell-sap  moves;  namely,  living  cells,  the 
wood-parenchyma  and  the  medullary 
rays  in  particular;  also  the  dead  ele- 
ments, vessels  and  tracheids.  Endos- 
mosis acts  as  a  propelling  force  in  a 
twofold  way  :  by  forcing  water  into  the 
dead  elements  at  one  point,  while  at 
some  more  elevated  point  the  living  cells 
take  up  the  same  and  conduct  it  for  a 
short  distance  from  cell  to  cell  by  endos- 
motic  suction.  This  proceeds  in  a  longi- 
tudinal direction  to  a  point  bearing  less 
water,  hence  upward,  where  it  will 
again  be  forced  into  the  tracheal  system. 
Capillarity  simply  acts  as  a  retaining 
force,  since  the  columns  of  water  are  self- 
supporting.2  In  the  remaining  explana- 
tions I  will  utilize  the  accompanying 
diagramatic  figure,  in  which  A,  B,  C, 
and  D  represent  different  elevations  in  FIG.  61. 

the  stem,  G  a  vessel,  m  the  medullary  rays,  kp  the  woody  paren- 


1  Berichte  der  Deutschen  Botaniscbeu  Gesellscbaft,  1883,  and  Sitz.-Ber.  der 
Berl.  Akad.,  1884. 

2  Zimmermann's  investigations  in  d.  Ber.  der  Deutsch.  Bot.  Ges.,  1883. 


110  COMPENDIUM  OF  GENERAL  BOTANY. 

chyma.  The  water-reservoir  of  the  root-system  extends  its  influence 
up  to  the  medullary  rays  at  the  levels  A.  It  is  only  necessary  that 
endosmosis  (suction)  should  act  from  cell  to  cell  through  the  paren- 
chyma until  the  medullary -ray  system  B  is  reached ;  here  the  water 
is  forced  into  the  vessel  until  it  rises  to  C.  From  there  on  endos- 
mosis  again  acts  within  the  parenchyma  as  far  as  the  medullary 
ray  in  D.  The  periodic  oscillations  in  the  bleeding-pressure 
observed  by  various  investigators  are  worthy  of  note.  We  may 
assume  also  that  in  reference  to  bleeding  a  minimum,  optimum, 
and  maximum  temperature  has  some  influence  on  this  process.1 

From  Schwendener's  communication  on  the  ascent  of  cell-sap 
the  following  important  statements  are  selected. ,  1.  Every  local 
suction  or  pressure  continues  to  act  only  in  those  particles  of  wood 
in  which  there  are  connecting  water- threads  or  columns.  2.  Break- 
ing of  the  water-columns  or  threads  by  air-bubbles  produces  a  high 
degree  of  immobility  within  the  vessels.  Air-bubbles  in  an  iso- 
lated vascular  tube  act  differently  from  those  in  a  tracheal  system. 
The  Jamin's  chain  already  referred  to  is  formed  in  the  vascular 
tube.  During  the  summer  the  bleeding-pressure  in  the  stem  of  a 
tree  will  allow  only  the  escape  of  sap  without  any  air-bubbles, 
even  when  vessels  and  tracheids  (libriform)  are  richly  supplied  with 
air.  This  wrater  (without  air-bubbles)  comes  from  the  tracheids, 
and  not  from  the  vessels.  The  resistance  in  the  Jamin-chain  within 
the  vessels  is  too  great  to  allow  bleeding-pressure  to  set  the  entire 
chain  in  motion.  However,  the  mass  of  water  can  move  onward 
through  the  pores  of  the  cell- walls  by  the  completion  of  the  water- 
column  through  laterally  uniting  water- columns  and  threads  in  the 
system  of  tracheids,  while  the  enclosed  air-bubbles  remain  station- 
ary. As  a  rule,  the  air-bubbles  are  in  the  middle  of  the  tracheids. 

The  ready  displacement  of  water  within  woody  tissues  suffi- 
ciently supplied  with  water  depends  upon  the  presence  of  continuous 
water-threads.  Placing  a  drop  of  water  upon  a  cross- section  of 
green  wood  several  metres  in  length  at  once  causes  the  escape  of  a 
drop  from  the  other  end  ("  HAKTIG'S  experiment  "). 

A  few  words  shall  be  added  concerning  the  effect  of  rarefied 
air,  in  other  words  concerning  the  physical  process  of  suction  (en- 
dosmosis)  within  the  wood. 


See  PFEFFER'S  Pflanzen physiologic. 


TISSUES  AND  SIMPLE  ORGANS.  Ill 

It  might  have  been  stated  above  that  high  negative  pressures 
have  not  been  observed  in  the  tracheal  system  at  a  considerable 
height  (of  a  tree) ;  neither  have  high  positive  pressures  been  ob- 
served in  the  lower  part  of  a  tree-trunk.  This  evidently  tends  to 
prove  that  capillarity  is  not  the  moving  force.  It  is  certain,  how- 
ever, that  spaces  containing  rarefied  air  do  occur  in  the  vessels  or 
in  the  tracheal  system.  The  question  that  arises  is,  What  can  en- 
dosmosis,  as  the  result  of  rarefying  air,  accomplish  in  the  tracheal 
system  by  way  of  elevating  water?  In  regard  to  this  question 
many  authors  hold  erroneous  opinions.  SCHWENDENEB,  ZIMMER- 
MANN,  *  and  GODLEWSKI  a  have  opposed  these  opinions.  I  will  here 
only  add  from  the  recent  work  of  Schwendener  8  that  the  lifting 
power  due  to  suction,  assuming  the  water-columns  to  be  10  mm. 
long  and  the  air-columns  to  be  of  equal  length,  may  be  from 
13  to  15  m.  However,  the  water-columns  observed  in  trees  after 
the  time  of  "  bleeding  "  were  much  less  than  10  mm. 

We  are  approaching  the  close  of  this  subject,  and  shall  now 
state  that  which  at  present  seems  to  be  the  authoritative  final  ex- 
planation of  the  water-movement  in  plants :  dead  elements  are 
essentially  the  paths  in  which  water  moves,  while  the  living  cells 
supply  the  propelling  force  for  the  transpiratory  current  of  water. 

Experiments  which  show  that  water  movements  in  a  living 
tree  will  also  continue  through  dead  segments  (killed  by  steaming, 
poisoning,  etc.)  do  not  prove  that  living  cells  are  unnecessary  to 
the  ascent  of  sap  (Schwendener) ;  such  dead  portions  presumably 
contain  more  than  the  usual  quantity  of  water  in  the  tracheal  sys- 
tem at  the  beginning  of  the  experiment,  later,  very  likely,  Jamin- 
chains. 

The  following  is  additional  evidence  of  the  correctness  of  the 
foregoing  fundamental  ideas :  the  contact  and  relation  of  commu- 
nication between  the  dead  tracheal  system  and  the  system  of  living 
cells  in  the  vascular  bundles  and  plant-organs;  the  occlusion  of 
vessel-lumina  by  means  of  tyloses  and  callus  in  the  case  of  injuries ; 
and  the  reduction  or  almost  entire  absence  of  vessels  in  submerged 
water-plants  whose  needs  for  a  water- conducting  system  are  very 


1  Ber.  der  Deutsch.  Bot.  Gesellsclmft  I,  1883. 
*  Pringsbeim's  Jahrbucber  XV,  1884. 

3  Zur  Kritik  der  neuesten  Untersuchungen  tiber  das  Saftsteigen,  Sitzungsber. 
der  Berl.  Akad.,  1892. 


112  COMPENDIUM  OF  GENERAL  BOTANY. 

small  or  nearly,  zero.  The  special  anatomical  structure  of  vascular 
walls,  namely  their  ability  to  withstand  the  high  radial  pressure 
which  proceeds  from  turgescent  cells,  can  only  strengthen  our  con- 
clusions. FRANK  '  calls  attention  to  the  fact  that  the  large  amount 
of  water  required  to  supply  the  numerous  leaves  in  the  spring  coin- 
cides with  an  adaptive  development  of  numerous  large  vessels  and 
tracheids. 

PEOTECTIVE  SHEATH  OE  ENDODEEM. 

(CONCLUDING  CHAPTER  TO  THE  THREE  FOREGOING  ONES  ON  SPECIAL- 
FUNCTIONS.  ) 

C  ASP  ART'S  term  protective  sheath  as  well  as  the  term  endo- 
derm  proposed  by  DE  BARY  are  equally  correct  designations  for  the 
tissue-system  under  consideration.  Normally  this  structure  occurs 
in  the  roots  ;  it  is  also  found  frequently  in  stem-organs,  even 
in  the  leaves.  Its  functions  are:  1.  Mechanical;  the  delicate 
elements  of  the  leptome  (albumen-conducting  tissues)  must  be  pro- 
tected against  injuries;  the  endoderm  encloses  these  delicate 
tissues  in  the  form  of  a  hollow  or  fluted  cylinder.  2.  In  case  of  the 
loss  of  the  peripheral  root-parenchyma  and  the  root-epidermis  it 
functions  in  their  stead  by  forming  a  protection  against  evapora- 
tion as  well  as  a  protective  tegumentary  covering.  3.  In  case  the 
root  remains  intact  it  restricts  the  interchange  of  cell -sap  in  the 
vascular  bundle  by  its  relative  impermeability  to  water-solutions. 
2  and  3  may  be  looked  upon  as  those  functions  which  would  make 
the  term  "  endoderm  "  (inner  tegument)  especially  applicable. 

The  following  statements  will  explain  the  nature  of  mechanical 
injuries  against  which  the  endoderm  forms  a  protection :  Delicate 
sieve-tube  tissues  are  subject  to  torsions  and  stretchings  due  to 
changes  in  turgor-pressure  within  the  contiguous  succulent  paren- 
chymatous  tissue.  If  these  lateral  and  longitudinal  tensions  pro- 
ceeding from  the  parenchyma  are  to  be  harmless  to  the  delicate 
sieve-tube  tissue,  they  must  be  enclosed  by  tissue-elements  which 
will  neutralize  or  counteract  these  tensions.  Thickening  of  the  cell- 
walls  of  the  endoderm  serves  to  supply  the  mechanical  requisites ; 
in  extreme  cases  the  ( c  simple  ' '  protective  sheath  receives  a  number 


Lehrbuch  der  Botanik,  Leipzig,  1892-1893. 


TISSUES  AND  SIMPLE  ORGANS.  113 

of  thick-walled  supporting  layers.  Suberized  walls  without  thick- 
ening very  frequently  assist  the  mechanical  function.  In  the  first 
place  it  is  a  mistake  to  suppose  that  completely  suberized  cell-walls 
are  in  general  very  extensible;  the  thin-walled  corky  layer  of 
birch-bark  proves  the  contrary.  (Actual  tests  in  regard  to  the 
elasticity  of  suberized  protective  sheath-cells  are  wanting.)  In  the 
second  place  we  may  ascribe  considerable  absolute  firmness  to  the 
suberized  cell- walls.  (Based  upon  actual  observation.) 

The  relative  impermeability  of  suberized  cell-walls  to  water- 
solutions  and  water-vapors  is  known  from  what  has  already  been 
stated. 

It  will  not  be  difficult  to  illustrate  what  has  been  said  of  these 
anatomical  relations  by  studying  a  dicotyledonous  and  a  monocoty- 
ledonous  root.  In  passing,  it  may  be  recalled  that  the  above 
mechanical  function  is  immediately  related  to  the  utilization  of 
thick- walled  cells  for  the  purpose  of  "  local  protection,"  as  was 
mentioned  in  the  discussion  of  the  mechanical  septum. 

The  root  of  A  Ilium  ascalonicum  (monocotyledon)   (Fig.    62) 


Fig.  62. — Central  vascular  system  of  the  root  of  Allium  ascalonicum. 

g,  Large  vessel;  s,  bundle-sheath  with  passage-cells  (transit-cells),  d;  p,  pericambium.    (After 

Haberlandt.) 

shows  the  protective  sheath  between  the  parenchyma  and  pericam- 
bium.     The  thick- walled  and  the  thin- walled  cells  of  the  protective 


114  COMPENDIUM  OF  GENERAL  BOTANY, 

sheath,  that  is,  the  characteristic  thickening  of  the  cell-walls  next 
to  the  leptome,  and  the  thin- walled  cells  (passage-cells  or  transit- 
cells)  which  form  the  c '  channels  ' '  of  communication  that  is,  points 
of  interchange  of  liquids  (cell-sap,  etc.),  between  the  parenchyma 
and  vessels.  Vicia  root  (Fig.  58)  shows  the  frequent,  but  not 
readily  understood,  formation  of  the  protective  sheath  as  it  usually 
occurs  in  dicotyledonous  roots  and  in  the  stems  of  water-plants. 
The  thin- walled  cells  of  the  protective  sheath  are  here  either  par- 
tially or  totally  suberized ;  in  the  former  case  only  the  radial  walls 
or  sometimes  only  the  middle  portions  or  bands  of  the  radial  walls ; 
even  with  such  partial  suberization  the  bands  form  a  continuous 
hollow  cylindrical  network.  In  its  mechanical  function  this  cylin- 
drical network  may  be  compared  to  the  protective  net-work  of 
rope  enclosing  a  balloon  (SCHWENDENER).  In  the  case  of  the  vas- 
cular bundle  of  the  root  the  pulling  tensions  are  of  course  on 
the  outside,  and  not  on  the  inside,  as  in  the  balloon.  The  follow- 
ing will  serve  to  explain  the  dark  spot  (u  Caspary's  dot  ")  seen  on 
the  radial  walls  in  cross-section  (Fig.  58).  They  are  local  thicken- 
ings of  the  cell- walls  (Caspary).  The  suberized  bands  of  the  cell- 
wall  are  only  slightly  extensible,  and  hence  only  slightly  contractile. 
The  unsuberized  walls  of  the  neighboring  cells  and  the  unsuberized 
portions  of  the  sheath-cells  are  highly  elastic  and  become  expanded 
by  the  turgor-force,  but  contract  again  as  soon  as  turgor  is  sus- 
pended ;  the  less  elastic  portions  can  only  adapt  themselves  to  this 
contraction  by  forming  wavy  foldings  (Schwendener).  These  wavy 
foldings  can  be  seen  in  tangential  sections.  The  dark  spot  seen  in  the 
cross-section  is  only  the  optical  effect  due  to  the  membranous  folding. 
When  the  tangential  walls  are  unsuberized,  the  above-mentioned 
"  limiting  "  or  "bounding  "  function  is  excluded  (see  3,  page  118). 

Roots  of  ferns  growing  upon  walls  and  rocks,  and  hence  exposed 
to  great  variations  in  the  supply  of  water,  have  enormously  devel- 
oped protective  sheaths.  (For  particulars  see  SCHWENDENER' s  com- 
munication on  Protective  Sheaths  and  their  Strengthenings.)1 

Without  in  any  way  interfering  with  subsequent  statements,  we 
shall  here  briefly  consider  SCHWENDENERV  more  recent  investiga- 
tions on  the  mestome-sheaths  of  gramineous  leaves.  The  phytoto- 


JDie  Schutzscheiden   und   ihre  Verstarkungen :    Abhandhmgen  der  Berliner 
Akademie,  1882. 


2  Sitzungsber.  der  Berl.  Akad.  1890. 


TISSUES  AND  SIMPLE  ORGANS.  115 

mist  in  the  study  of  the  leaf  anatomy  frequently  observes  that  the 
vascular  bundles,  especially  of  the  monocotyledons,  are  supplied 
with  a  thickened  endoderm  (mestome-sheath),  and  in  addition,  im- 
mediately outside  of  the  same,  a  ' '  parenchymatous  sheath,"  which 
is  usually  chlorophyll-bearing  and  which  we  have  already  referred 
to  in  the  discussion  of  the  conducting  system.  As  examples  in 
which  this  occurs  we  may  mention  Pod  pratensis  and  Bambu&a 
vulgaris.  In  the  absence  of  the  mestoine- sheath  it  frequently 
happens  that  the  parenchyma-sheath,  although  belonging  to  the 
conducting  system,  shows  modifications  in  its  structure  (thickening 
of  walls,  suberization,  etc.)  which  enable  it  to  perform  the  function 
of  the  endoderm.  Vice  versa  it  may  happen  that  in  the  absence  of 
the  endoderm  a  part  of  the  mestome-cells,  especially  a  crescent- 
shaped  group  of  the  leptsome-parenchyma,  may  become  thickened 
and  so  perform  a  mechanical  function. 

Y.  PROTECTION  OF  THE   MERISTEMATIO  AREAS  OF 
THE  PLANT-BODY. 

Young,  undeveloped  leaves  perform  a  service  for  the  apical 
area  of  the  stem  similar  to  that  which  the  root- cap  performs  for 
the  root-apex.  The  rolling-in  of  the  young  leaves  of  ferns  serves 
a  purpose  similar  to  that  which  sinking-in  of  the  apical  area  does 
in  the  algse  (Fucus,  Laurencia).  The  leaf -sheaths  of  grasses  and 
Eqv/isetc&i  and  the  sheath  enclosing  the  growing  peduncle  of  Arme- 
ria,  serve  a  similar  function  for  the  internodes  which  they  enclose 
as  does  the  collenchyma  in  firm  growing  tissues.  With  these 
statements  we  have  hastily  sketched  the  teleological  significance  of 
the  subject  under  discussion.  In  all  cases  we  are  concerned  with 
the  protection  of  delicate  meristematic  tissues  against  definite 
mechanical  injuries  as  well  as  against  injuries  in  general. 

The  special  consideration  of  individual  cases  will  give  us  an 
opportunity  to  mention  important  facts  pertaining  to  the  develop- 
ment of  the  leaf. 

(a)  The  Protection  for  Terminal  Meristematic  Areas  of  the 

Plant-body. 

a.  Protection  of  the  Root-tip. 

The  growing  root-tip  forcing  its  way  between  particles  of  soil  is 
supplied  with  a  specific  protective  organ,  namely,  a  bell-shaped 


116 


COMPENDIUM  OF  GENERAL  BOTANY. 


tissue  generated  from  the  interior,  but  the  history  of  its  growth  and 
development  may  differ  very  much  in  different  cases.  Behind  the 
root-cap,  as  this  organ  is  called,  lies  the  true  root-lody,  which  is 
especially  adapted  by  the  numerous  root-hairs  on  the  outer  surface 


FIG.  63. — Longitudinal  section  of  the  root-tip  of  Eriophorum  vaginatum. 
z,  c,  Root-cap ;   e,  epidermis;  r,  parenchyma;  p,  vascular  system.    (After  Haberlandt.) 

to  take  up  food-substances.  The  root-cap  therefore  covers  the 
cell-forming  vegetative  area,  which  could  not  withstand  the  friction 
caused  by  contact  with  the  sharp-angled  particles  of  earth. 

The  root-cap  may  1.  develop  from  a  formative  tissue  designed 
for  that  purpose ;  examples:  Triticum  repens  (or),  Calla palustris 
(/?.)  In  type  (a)  there  is  a  sharp  distinction  between  the  meristem 
of  the  root  and  that  of  the  root-cap ;  in  type  (0)  there  is  no  such 
distinction. 

2.  These  two  types  among  monocotyledons  are  represented  by 
two  corresponding  types  among  dicotyledons,  but  which  differ  es- 


TISSUES  AND  SIMPLE  ORGANS. 


117 


sentially  in  that  it  is  the  epidermis  of  the  root  from  which  the  root- 
cap  is  developed  by  centripetal 
cell-division  and  branching. 
In  this  case  the  tissue  which 
forms  the  root-cap  bears  root- 
hairs  at  some  distance  behind 
the  tip  of  the  root.  If  we 
designate  the  tissue  which 
forms  the  root-cap  of  dicoty- 
ledons as  calyptrogen,  that  of 
monocotyledons  should  be 
called  ' '  dermocalyptrogen. ' ' 
The  Helianihus  or  Brassica 
type  corresponds  to  1  a,  that 
of  Pisum  to  1  /3. 

3.  The  parenchyma,  either 
the  outer  layers  or  the  entire 
tissue,   may  form  the  root-cap 
by  the  branching  of  the  cell- 
layers,  as  in  the  gymnosperms 
Juglans  regia  and  Ccesalpinia 
brasiliensis. 

4.  The  apical  cell  (event- 


FIG.  64.— Root-tip  of  Lepidium  sativum. 
ep,  Epidermis.    (After  Schwendener.) 


FIG.  65. — From  the  root-tip  of  Cytisus  racemosus. 
ep,  Epidermis.     (After  Schwendener.) 


118 


COMPENDIUM  OF  GENERAL  BOTANY. 


ually  the  four  apical  cells  arranged  in  a  quadrant)  forms  cells 
("  segments  ")  toward  the  side  of  the  root;  occasionally  also  cells* 
("  root-cap  segments")  which  form  the  root-cap:  ferns  and 
Equisetum. 

Fig.  63  represents  type  1  <*,  Fig.  64  type  2  a,  Fig.  65  type 
2  /3.     The  fern  type  is  represented  in  Fig.  29,  p.  47. 

ft.   The  Protection  of  the  Stem-apex. 

1.   Normally  the  apical  area  of  the  stem  has  no  specific  organ 

which   serves   as   a  protective   covering   for   its   vegetative  area, 

although  it  is  evidently  in  need 
of  one  ;  such  protection  is  sup- 
plied by  the  young  leaf-bud, 
which  forms  a  covering  of 
mcmy  layers.  Fig.  66  a  illus- 
trates this  condition.  Numer- 
ous examples  of  this  kind 
may  be  observed  in  longitu- 
dinal sections  of  leaf-buds, 
bulbs,  etc.  Fig.  66  ~b  is  in- 
tended to  represent  in  general 
a  longitudinal  section  of  a 
stem  with  blunt  apical  area. 
Besides  these  most  common 
forms  of  protection,  there  are 
a  few  others,  namely  : 

2.  The  depression  of  the 
apical  area;  example,  algae, 
in  which  the  apical  cell  lies 
at  the  bottom  of  a  hollow 
or  depression  (JFucacecti)  \  we 
may  also  mention  inferior 
ovaries  (cup-shaped  receptacle 
or  torus).  From  a  physiolog- 
ical standpoint  we  must  also 

include  the  morphological  rule  that  normal  lateral    buds  appear 

axillary,  that  is,  in  the  axis  of  a  leaf. 

3.   Protection  by  means  of  rolling  in  is  shown  in  Floridem 

(red  marine  algae). 


TISSUES  AND  SIMPLE  ORGANS, 
y.  Protection  of  the  Leaf -tip. 


119 


The  following  is  immediately  associated  with  what  has  just 
been  stated  (3).  An  interesting  and  at  the  same  time  easily 
demonstrable  means  for  the  protection  of  growing  organs  is  to  be 
found  in  leaves  of  ferns.  The  leaves  of  the  ferns  are  an  exception 


FIG.  66  b.— (Diagramatic.) 

to  those  of  numberless  other  plants  in  their  mode  of  development 
(Wedel).  Most  leaves  (phanerogams)  develop  so  that  the  tip  or  apex 
ceases  to  grow  first,  the  base  last.  In  this  and  in  the  overlapping 
of  the  leaves  in  the  bud  lies  the  protection  for  the  meristematic 
portions  of  these  organs.  Fern-leaves,  however,  are  peculiar  in 
having  a  long-continued  apical  growth  from  an  apical  cell :  the  tip 
therefore  requires  some  form  of  protection  for  a  considerable  period 
of  time ;  this  is  supplied  by  the  well-known  spiral  (circinate)  rolling 
of  the  leaf -tips. 

(b)  Protection  for  Areas  of  Intercalary  Growth. 

In  this  category  of  protective  adaptations  we  are  in  part  con- 
cerned with  evident  mechanical  relations.  Accordingly  at  least  a 
part  of  this  discussion  might  have  found  a  place  in  the  treatment 
of  the  mechanical  tissue-system.  I  believe,  however,  that  it  may 
well  be  introduced  at  this  point.  In  the  first  instance  we  are  con- 
cerned with  firm  organs,  stems  in  particular,  which  become  elon- 
gated at  interpolated  zones  ("  intercalation  ").  It  is  evident  that 
these  growing  zones  consist  of  delicate  and  yielding  tissues ;  there- 


120  COMPENDIUM  OF  GENERAL  BOTANY. 

fore  they  represent  the  weakest  points  in  the  mechanical  structure 
of  the  stem.  At  these  points  bending  or  breaking,  due  to  lateral 
forces,  would  most  readily  take  place.  The  adaptations  which 
occur  in  the  plant  creation  to  protect  this  process  of  growth  by 
intercalation  were  also  revealed  by  SCHWENDENER'S  investigations, 
concluded  in  1874. 

There  are  two  essential  means  for  securing  this  protection.  In 
the  one  case  it  is  the  employment  of  a  special  tissue-system  with 
specific  physiological  properties.  As  is  known,  typical  mechanical 
cells  are  either  lifeless  or  at  least  incapable  of  elongating  after  they 
have  once  acquired  their  extensive  wall-thickenings;  they  can 
therefore  not  exist  in  growing  organs.  This  special  mechanical 
tissue  is  the  collenchyma,  which  we  learned  to  know  in  the  chapter 
on  the  cell.  It  is  very  readily  recognized  by  the  characteristic 
thickenings  of  the  angles  of  the  cell- wall.  In  spite  of  these  thick- 
enings it  is  capable  of  growth.  This  tissue  has  approximately  the 


FIG.  67.— Cross-section  of  the  leaf-sheath  of  Brachypodium  silvaticum. 
(After  Haberlandt.) 

same  firmness  (extensibility)  as  the  typical  mechanical  tissue,  but  is 
peculiar  in  that  it  becomes  permanently  elongated  (without  tearing) 
wrhen  subjected  to  a  slight  pulling  force  (AMBRONN).  Collenchyma 
frequently  serves  to  strengthen  the  growing  internodes  of  dicoty- 
ledonous stems  (Compositce,  Umbelliferce,  Labiatece,  etc.).  This 
arrangement  may  in  many  cases  be  combined  with  the  second  form 
of  protective  adaptation,  which  we  shall  now  consider. 

The  envelopment  of  the  growing  stem  by  supporting  tubes  is 
of  very  frequent  occurrence  among  monocotyledons,  less  frequent 


TISSUES  AND  SIMPLE  ORGANS. 


121 


among  dicotyledons.  The  leaf-sheaths  of  Graminece,  Cyperacece, 
and  of  EquisetcB  perform  this  function  by  enclosing  the  growing 
(as  a  rule  the  basal)  portion  of  the  internode  from  which  the  node 
projects  after  it  has  become  sufficiently  strengthened.  The  nodes 
of  grass-stems,  and  also  the  region  above,  are  interesting  structures 
for  investigation  and  study;  some  of  their  peculiarities,  especially 
geotropic  curvatures,  will  be  discussed  later.  Fig.  67  and  68  will 
aid  in  explaining  what  has  just  been  said  and  that  which  is  to 
follow. 

In  Fig.  68  the  typical  mechanical  tissue  which  has  lost  the 
power  of  growth  is  colored  black.  The  supporting  tube  (leaf- 
sheath)  s  encloses  the  yet  weak  and 
cambial  base  of  the  stem  h ;  s  extends 
above  the  cambial  portion  of  the  inter- 
node.  At  co  the  mechanical  tissue- 
system  is  not  composed  of  typical  bast 
but  of  collenchyma,  therefore  capable 
of  growth.  If  a  grass-stem  is  placed 
in  a  horizontal  position,  the  more  rapid 
growth  of  the  lower  side  of  this  collen- 
chymatous  node  will  cause  it  to  rise  to 
a  vertical  position.  The  firm  and  more 
mature  portion  of  the  stem  within  co  is 
thereby  passively  bent. 

A  rare  case,  occurring  so  far  as 
known  only  in  the  genus  Armeria,1 
has  been  observed  and  may  be  briefly 
mentioned.  The  mechanical  sheath  of 
bracts  at  the  base  of  the  inflorescence 
extends  from  above  downward ;  the 
growing  part  of  the  peduncle  lies  at  the 
upper  end  of  the  internode.  The 
sheath  is  completely  formed  in  the 
young  plant,  and  after  the  peduncle  has  completed  its  growth  it 
dries  up  and  finally  becomes  torn. 


FIG.    68.— Longitudinal  section 
through  the  node  of  a  grass- 
stem. 
(Diagramatic  after  Schwendener.) 


1  Reported  by  the  author  in  1881  (Monatsber.  der  Berl.  Akad.).  Professor 
Schwendener,  who  has  doue  so  much  for  scientific  teleology,  during  on<?  of  his  ex- 
cursions in  the  vicinity  of  Berlin,  expressed  an  opinion,  as  to  what  was  probably 
the  true  state  of  the  case,  which  led  me  to  make  more  exact  investigations. 


122  COMPENDIUM  OF  GENERAL  BOTANY. 

A  third  means  of  protecting  areas  of  intercalary  growth  may 
be  mentioned,  namely,  the  increase  in  diameter  in  the  region  of 
the  growing  zone.  Tradescantia  erecta,  according  to  Sehwen- 
dener,  is  one  of  those  plants  in  which  basal  growth  of  the  inter- 
node  takes  place ;  it  has  internodes  in  the  form  of  truncate  cones. 
Exact  measurements  in  regard  to  the  course  of  intercalary  growth 
have  not  yet  been  made. 

With  reference  to  the  intercalary  (basal)  growing  leaves,  which 
include  the  great  majority  of  leaves,  it  may  be  stated  briefly  that 
the  growing  areas  are  protected  by  the  enveloping  sheath-like  leaf- 
blades  (elongated  monocotyledonous  leaves)  as  well  as  the  overlap- 
ping of  the  leaves  in  the  bud  (dicotyledonous  leaves). 

Among  conifers  there  are  membranous  sheaths  consisting  of 
the  bud-scales  which  enclose  the  leaf -base. 

VI.    FOOD-SUBSTANCES    DEBITED    FEOM    THE    AT- 

MOSPHEEE.     ASSIMILATION  OF  CABBON 

IN  GEEEN  OEGANS. 

The  dry  (solid)  substance  of  the  plant-body  is,  for  the  most 
part,  the  transformation  product  of  atmospheric  carbonic  acid  (CO2, 
carbon  dioxide).  Pure  carbon  (C)  constitutes  about  one-half  of 
this  dry  substance,  and  is  found  in  chemical  union  in  the  cellulose 
of  membranes,  in  starch-grains,  in  fats,  in  plasm,  etc.  C  appears 
in  the  green  organs  as  gaseous  COa.  CO2  unites  with  the  elements 
of  water  (H2O)  through  the  influence  of  sunlight  on  chlorophyll, 
forming  starch  or  some  allied  compound  and  setting  free  oxygen  (O). 
These  transformations  take  place  in  a  very  short  period  of  time. 
The  greater  part  of  the  plant-body  (plasm  and  cell-walls)  is  there- 
fore derived  from  the  atmosphere. 

That  carbon  dioxide  and  water  form  the  starting-points  for  the 
production  of  starch  as  well  as  for  other  related  substances,  with 
liberation  of  O,  is  well  known;  also  that  these  transformations 
may  take  place  in  a  few  hours  or  minutes.  But  the  most  discern- 
ing chemists  at  present  refrain  from  attempting  to  explain  the 
individual  chemical  reactions  involved  in  the  important  processes 
of  assimilation.  In  general,  the  following  formula  may  be  con- 
sidered as  correct:  12CO2  +  10II.O  =  cC2H20O10  (starch)  +  O24 , 
while  the  gas- volumes  remain  nearly  the  same. 


TISSUES  AND  SIMPLE  ORGANS.  123 

The  most  important  bearers  of  the  assimilating  function  are  the 
chlorophyll-bodies,  which  have  a  discoid  form,  among  algae  a  band- 
like,  flattened  or  stellate  structure.  A  definite  tissue  in  which  they 
may  occur  is  not  always  necessary,  though  we  usually  speak  of  assim- 
ilating cells,  forming  a  specific  assimilating  tissue  which  is  found 
in  the  true  assimilating  organs,  the  green  leaves.  The  principles 
which  underlie  and  regulate  the  function  of  chlorophyll-bodies, 
that  is,  the  conditions  under  which  they  can  perform  their  most 
favorable  activity,  also  underlie  the  structure  of  the  tissues  and  the 
organs  which  serve  the  function  of  assimilation.  We  will  there- 
fore next  consider  the  structure  of  the  assimilating  tissue-system. 

(a)  The  Structural  Principles  of  the  Assimilating  System. 

G.  HABERLANDT  and  STAHL  have  within  more  recent  times 
made  important  investigations  in  regard  to  the  physiological  anat- 
omy of  assimilation ;  to  these,  among  others,  must  be  added  the 
communications  of  HEINRICHER.  From  &  physiological  standpoint 
the  communications  of  SACHS  are  the  most  important. 

The  Greatest  Possible  Utilization  of  the  Luminous  Effects  of 
Sunlight  by  the  Chlorophyll. — Following  in  thought  the  problem 
suggested  by  this  statement  leads  us  to  the  essential  points  of  view 
which  give  us  a  physiological  understanding  of  the  structure  of  the 
assimilating  organs.  When  I  say  ' '  greatest  possible  ' '  utilization 
of  sunlight,  I  wish  to  explain,  in  order  to  avoid  erroneous  concep- 
tions, that  the  nature  of  chlorophyll  is  such  that  assimilation  reaches 
its  optimum  with  certain  light-intensities;  beyond  these  an  injurious 
influence  makes  itself  felt.  Similarly  with  the  amount  of  CO2 
present :  increasing  it  to  8  per  cent  with  high  intensity  of  light 
there  is  still  noticeable  an  increase  in  assimilation.  Physiology 
must  here  likewise  be  satisfied  with  a  causal-final  or  teleological  ex- 
planation of  the  anatomical  adaptations ;  a  causal-mechanical  ex- 
planation is  impossible. 

The  principle  of  the  surface  expansion  of  the  leaf  which  mani- 
fests itself  by  the  outer  form  is  still  more  evident  in  its  anatomi- 
cal structure  (Figs.  69,  TO,  71).  A  maximum  expansion  of  cell- 
surface  is  obtained  by  membrane-foldings,  by  the  regular  form  and 
large  numbers  of  assimilating  cells.  Such  adaptive  arrangements 
make  room  for  the  numerous  chlorophyll -grains  which  are  always 
adjacent  to  the  cell-wall.  The  regular,  elongated  palisade-cells. 


124  COMPENDIUM  OF  GENERAL  BOTANY. 

with  their  extensive  cell-wall  areas,  the  4 '  arm-palisade  ' '  with  its 
foldings  (or  incomplete  cell-walls),  are  also  formed  on  the  principle 
of  great  surface  expansion.  It  is  of  course  necessary  that  these 
cell-wall  surfaces  occur  on  the  side  of  the  leaf  exposed  to  sunlight. 

The  arrangement  of  these  walls  and  their  foldings  are  also  to  be 
considered  in  their  relation  to  other  requirements ;  first  of  all  they 
serve  to  conduct  the  products  of  assimilation  by  the  shortest  route 
possible,  and  at  the  same  time  permit  light  to  pass  to  the  more 
deeply  seated  cell-layers.  There  is,  no  doubt,  a  reciprocal  relation- 
ship between  the  light-intensity  and  the  perfection  of  the  assimila- 
tory  tissue-system,  in  that  the  constant  lateral  position  of  the 
chlorophyll-bodies  in  the  palisade-cells  (movement  of  the  chloro- 
phyll-grains within  the  palisade-cells  is  only  an  exceptional  phe- 
nomenon) is  most  suitable  for  strong  light-intensities  (Stahl). 
However,  the  structural  conformation  to  strong  light-intensities  does 
not  take  a  higher  rank  than  that  for  conveying  food-substances  by 
the  shortest  route  possible  (Haberlandt).  That  the  latter  is  indeed 
a  principle  of  prime  importance  can  be  seen  by  glancing  at  the 
figure  of  Silphium  laciniatum  (72) ;  further,  also,  from  the  fact 
that  there  is  a  group  of  plants  in  which  the  assimilating  cells  are  at 
the  same  time  conducting  cells ;  they  extend  parallel  to  the  leaf- 
surface,  either  in  a  direction  toward  the  leaf -base  or  toward  the 
median  vein  (leafy  mosses,  some  monocotyledons). 

In  the  case  of  Silphium  (see  Fig.  72)  we  can  see  that  the  posi- 
tions of  the  cell-wall  bounding  the  intercellular  spaces  (2),  although 
eventually  exposed  to  strong  illumination,  are  lined  with  chloro- 
phyll-grains, while  the  portions  of  the  cell-wall  which  cross  the 
current  of  assimilates  at  right  angles  are  free  from  them :  this  is 
an  example  of  the  predominance  of  the  principle  of  conduction. 

Finally,  there  are  cases  in  which  the  palisade- cells  are  radiately 
arranged  about  a  vascular  bundle,  which  unmistakably  indicates 
that  the  principle  of  conduction  by  the  shortest  route  possible  is  of 
prime  importance.  The  palisade-cell  placed  at  right  angles  to  the 
leaf-surface  is  only  a  very  frequent  special  case  in  the  series  of 
elongated  assimilating  cells. 

With  reference  to  these  adaptive  relations  we  shall,  with 
HABERLANDT,  place  the  arrangement  and  position  of  the  palisade- 
cells  under  the  principle  of  conduction  by  the  shortest  path.  STAHL 
is  inclined  to  consider  the  adaptation  to  light-intensities  as  the  most 


TISSUES  AND  SIMPLE  ORGANS. 


125 


FIG.  69  A.— Vertical  section  through 
the  leaf  of  Sambucus  nigra.  "  Arm- 
palisades.  " 

(After  Haberlandt.) 


FIG.  71. — Vertical    section   through 
the  leaf  of  Juglans  regia. 

Palisade-cells  are  supposed  to  be  richly, 
the  spongy  tissue  cells  less  richly,  sup- 
plied with  chlorophyll.  Both  cell-forms 
are  here  typically  developed.  (After 
Haberlandt.) 


FIG.  69  B. — Vertical  section  through  the  leaf,  including  the  midrib,  of  Rapha- 

nus  sativus. 
(After  Haberlandt.) 


]?IG  70.  —  Vertical  section  through  the  leaf  of  Ficus 
elastica.     The  epidermis  is  omitted. 


v  and  pi,  Palisade-cells  ;  a,  collecting  cells  ;  s.  p 

sheath  ;  y,  vascular  bundle.    (After  Haberlandt.; 


FIG.  72. — Lower  surface  of 
an  *'  isohiternl  "  leaf,  Sil- 
phi'iim  laciniatum. 
(After  Haberlandt.) 


126         COMPENDIUM  OF  GENERAL  BOTANY. 

important.  Nor  do  we  deny  the  correlation  of  the  adaptations. 
The  arrangements  of  the  palisade-cells  at  right  angles  to  the  leaf- 
surface  is  the  most  common  position  of  assimilating  cells,  because 
here  illumination  is  as  a  rule  most  perfect  or  intense ;  furthermore, 
the  adaptive  development  of  one  side  favorable  to  light  in  leaves 
illumined  on  one  side,  and  the  adaptive  development  of  two  sides 
favorable  to  light  in  leaves  illumined  on  both  sides  (isolateral  leaves), 
are  additional  evidence  of  this  correlation,  and,  in  general,  the  cor- 
relative arrangement  of  typical  assimilating  cells.  Finally,  light-in- 
tensity and  anatomical  structure  give  expression  to  this  correlation 
in  the  differences  of  sun-leaves  and  shade-leaves  which  develop  on 
the  same  plant  or  plant  species.  The  difference  is  particularly 
noticeable  in  the  stronger  development  of  the  palisade-tissue  in  the 
sun-leaf  (Stahl). 

In  addition  to  the  two  structural  principles  of  HABEKLANDT — 
surface  expansion  and  shortest  path  for  the  assimilates — we  may  add 
a  third  structural  principle  harmonizing  with  existing  facts,  namely, 
Stahl 's  principle  of  the  adaptation  to  light-intensity.  From  the 
above  arguments  we  must  consider  this  relation  to  light  as  a  struc- 
tural principle  belonging  to  this  chapter.  In  one  respect  these  three 
principles  are  very  much  alike :  all  are  readily  understood  from 
a  teleological  standpoint,  not  one  is  explained  casual  mechanically. 
The  factor  light  must  invariably  be  brought  into  consideration. 

Below  the  palisade-cells  of  the  luminous  side  of  an  ordinary 
horizontal  leaf  lies  the  loose  spongy  tissue,  so  named,  because  of  the 
large  intercellular  spaces  and  irregular  cell-forms.  This  structure, 
which  is  also  shown  in  the  accompanying  figures,  is  characteristic 
of  the  lower  surface  of  the  leaf.  It  evidently  serves  to  perform 
several  functions :  (a)  the  conveying  of  the  products  of  assimilation 
to  the  parenchyma-sheaths  of  the  vascular  bundles ;  when  the  proc- 
esses of  differentiation  have  progressed  somewhat  more,  we  may 
also  distinguish  "  collecting  cells  "  (see  Fig.  70,  a);  (5)  an  assimi- 
lating activity  because  of  the  chlorophyll  present.  We  must  also 
bear  in  mind  the  self-evident  result  of  the  bounding  of  numerous 
cells  by  intercellular  air-spaces,  that  is,  considerable  transpiration 
must  take  place.  The  author,  however,  agrees  with  YOLKENS 
who  looks  upon  this  transpiration  as  a  process  physically  necessary 
and  which  produces  physiological  effects,  but  which  in  itself  is  not 
a  physiological  function.  We  must,  however,  ascribe  to  the 


TISSUES  AND  SIMPLE  ORGANS.  127 

spongy  tissue  a  third  essential  function,  namely,  the  aeration  of 
the  typical  assimilating  tissue  (the  palisades).  The  latter  contains 
numerous  but  narrow  air-channels  which  are  arranged  about  each 
palisade- cell ;  but  the  supply  of  CO2  and  the  nearest  centres  of 
accumulation  for  the  liberated  O  are  naturally  to  be  sought  for  in 
the  spongy  tissue,  since  it  communicates  directly  with  the  atmos- 
phere. Particulars  will  be  given  below  (VII.,  Special  Function). 

The  teleological  consideration  of  nature  suggests  that  not  all 
leaves  met  with  in  nature  are  built  ' '  bif acially  ' '  and  equipped 
with  anatomically  different  light-  and  shade-surfaces.  Observation 
teaches  that  beside  the  large  number  of  flat  leaves  placed  horizon- 
tally there  are  many  of  cylindrical  form  (linear  leaves),  and  others 
which  are  flat,  but  not  horizontal,  either  having  the  margin  turned 
toward  the  stem  (CalUstemon,  Lactuca  scariola)  or  placed  ap- 
proximately vertical.  The  latter  position  occurs  among  some 
grasses,  among  orchids,  in  Acorns,  etc.  From  this  may  be  deduced 
the  following :  1 

A.  A  "centric"  type  of  structure  with  a  two-sided  or  cylin- 
drical evenly  developed  chlorophyll-bearing  parenchyma  is  peculiar 
to  those  flat  leaves  not  horizontally  placed,  as  many  grasses,   or- 
chids, Acorus,  Lactuca  scariola,  Callistemon,  etc.   (see  Fig.   72). 
Also  those   leaves  approximately   cylindrical — needles,    so  called. 
To  the  latter  should  also  be  added  the  green  culm-like  stems  (hal- 
martige  /Stengel). 

B.  The  majority  of  leaves  belong  to  the  bifacial  type  and  are 
always  flat  and  placed  horizontally.     I  shall  not  hesitate  in  citing  a 
very  striking  example  of  adaptive  phenomenon.     The  leaves  of 
Allium  ursinum,  Alstrwmeria,  and  others,  in  their  early  develop- 
ment cause  the  morphologically  lower  surface  of  the  leaf  to  be 
turned  upward  by  a  torsion  of  180°  of  the  petiole  or  leaf -basis.     In 
these    leaves    the    morphologically    lower    surface    possesses   the 
structural   arrangements    for    active    assimilation.     An   analogous 
example  has  been  observed  by  SCHWENDENER  in  the  mechanical 
adaptation  of  the  leaf  of  Gynerium  argenteum. 

The  same  physiological  significance  as  that  of  the  mormal  bifa- 
cial leaf-structure  also  underlies  the  fact  that  in  the  lichens  the 
assimilating  algal  cells  ("gonidia")  are  found  nearest  the  luminous 
side  of  the  leaf -like  thallus  (see  the  chapter  on  symbiosis). 

1  DE  BARY,  Comparative  Anatomy,  page  406,  et  seq. 


128  COMPENDIUM  OF  GENERAL  BOTANY. 

The  physiology  of  the  phenomena  of  movements  will  acquaint 
us  with  adaptive  movements  which  will  bring  the  leaves  into  the 
most  suitable  positions  with  reference  to  the  sunlight.  The  chloro- 
phyll-bodies themselves  have  special  adaptations  for  the  maximum 
utilization  of  the  sun's  rays. 

(5)  Movements  and  Changes  in  Form  of  Chlorophyll-bodies. 

According  to  STAHL,  the  chlorophyll-bodies  among  certain  forms 
of  the  so-called  lower  plants  (filamentous  algse)  are  capable  of  move- 
ment. In  Mesocarpus  each  cell  possesses  a  rotating  chlorophyll- 
plate  which  bisects  the  cell  longitudinally.  In  diffuse  sunlight  the 
flat  surface  is  turned  toward  the  light,  while  toward  the  rays  of 
direct  insolation  a  profile  position  is  assumed.  In  the  single- 
layered  leaves  of  the  moss  Funaria  hygrometrica  the  chlorophyll- 
bodies  assume  a  position  along  the  lateral  walls  (profile  exposure)  in 
direct  sunlight  as  well  as  in  the  dark,  while  in  the  ordinary  diffuse 
sunlight  they  are  adjacent  to  the  outer  walls  (surface  exposure). 
In  the  palisade-cells  of  the  higher  plants  it  has  been  observed 
(mainly  according  to  STAHL)  that  the  approximately  hemispherical 
chlorophyll-bodies  with  their  flattened  surfaces  directed  toward  the 
cell-wall  (longitudinal)  extend,  that  is,  elongate,  somewhat  more 
into  the  interior  of  the  cell  in  diffuse  sunlight,  while  in  direct  sun- 
light they  lie  more  closely  in  contact  with  the  cell -wall  and  increase 
their  diameter  in  the  direction  of  the  adhering  surface.  Covering 
a  leaf-portion  with  tinfoil  causes  this  part  to  become  more  dark- 
green  as  compared  with  the  strongly  illumined  portions  (SACHS). 

The  following  deductions  may  be  drawn  from  the  three  phe- 
nomena illustrated  by  the  above  examples,  namely,  the  rotating  of 
the  chlorophyll-plate,  and  the  movements  and  change  in  form  of 
the  chlorophyll-bodies:  1.  Chlorophyll  is  enabled  to  derive  a 
maximum  benefit  from  definite  light-intensities  by  enlarging  its 
surface  area.  2.  It  protects  itself  against  light-rays  of  too  great 
intensity,  very  probably  because  it  would  thereby  be  injured  in  its 
function  and  composition.  According  to  PKINGSHEIM,  chlorophyll 
is  destroyed  by  concentrated  sunlight  in  the  presence  of  oxygen. 

(c)  The  Chemistry  and  Physiology  of  Chlorophyll. 

The  exact  chemical  composition  of  the  green  coloring  substances 
designated  as  chlorophyll  is  but  little  understood.  It  contains  the 


TISSUES  AND  SIMPLE  ORGANS.  129 

elements  (7,  //,  6>,  and  N,  iron  is  necessary  to  its  development  (as 
well  as  to  its  composition?).  The  plasmatic  colorless  or  nearly 
colorless  basal  substance  (stroma)  of  the  chlorophyll-body  is  tinged 
with  the  green  coloring  substance ;  this  latter  can  be  extracted  with 
alcohol.  The  delicate  structure  of  this  fundamental  substance 
according  to  more  recent  authors  is  said  to  be  spongy,  not  homoge- 
neous. The  fact  that  chlorophyll-bodies  divide  has  been  known 
for  some  time.  Further,  it  has  been  supposed  by  many  authors 
that  two  coloring  substances,  a  green  and  a  yellow,  are  present  in 
the  chlorophyll-bodies  (according  to  earlier  investigators,  blue  and 
yellow).  The  foregoing  statements  represent,  so  to  speak,  succes- 
sive stages,  which  are  not  yet  concluded,  of  the  attempts  made  to 
find  the. chemical  and  physical  structure  of  chlorophyll-bodies.  It 
is  to  be  kept  in  mind  at  present  that  chlorophyll  is  a  green-colored 
plasm  of  highly  characteristic  properties  which  manifest  themselves 
in  the  work  of  assimilation. 

In  regard  to  this  work  of  assimilation  we  must,  in  view  of 
the  results  obtained  by  ENGELMANN  (Utrecht),  admit  that  con- 
siderable progress  has  been  made.  The  theory  of  the  physicist 
LOMMEL  that  the  rays  which  are  absorbed  by  the  chlorophyll-spec- 
trum are  most  active  in  assimilation  seems  to  have  been  verified  by 
Engelmann.  The  method  of  investigation  of  this  latter  physiolo- 
gist is  in  itself  very  interesting.  It  is  called  the  ' '  bacteria  method, ' ' 
and  consists  in  its  essentials  of  the  utilization  of  sensitive  bacteria 
suspended  in  a  drop  of  water.  The  bacteria  accumulate  where 
there  is  a  supply  of  oxygen.  An  assimilating  cell-thread  under 
the  microscope  is  observed  under  such  environments  as  expose  it 
to  the  seven  colors  of  the  solar  spectrum  which  are  projected  side 
by  side  on  the  long  axis  of  the  thread ;  the  surrounding  liquid  con- 
tains the  sensitive  bacteria ;  they  accumulate  most  at  the  points  of 
maximum  assimilation,  hence  where  the  most  oxygen  is  liberated. 
These  experiments  show  that  the  two  optima  of  assimilation  (as 
judged  by  the  liberation  of  oxygen)  occur  first  in  the  red  and  a 
second  smaller  optimum  occurs  in  the  highly  refrangible  parts  of 
the  spectrum  :  blue,  violet,  and  ultra-violet ;  it  is  in  these  spectral 
areas  that  the  characteristic  absorption-bands  of  chlorophyll  lie 
(similar  to  those  of  living  chlorophyll).  (The  optimum  of  assimila- 
tion in  the  red  [orange]  had  been  observed  by  BEINKE,  previous  to 
the  investigations  of  Engelmann,  and  still  earlier  by  ~N.  J.  C. 


130  COMPENDIUM  OF  GENERAL  BOTANY 

MULLER).  All  observers  agree  that  assimilation  is  much  less 
active  in  the  more  strongly  refrangible  half  of  the  spectrum — uni- 
formly designated  as  ' '  chemical  rays ' '  (actinic  rays)  because  they 
induce  certain  chemical  processes — than  in  the  less  refrangible  half. 
The  above  coincidence  of  light-absorption  and  assimilation  in  the 
chlorophyll-bodies  harmonizes  with  the  supposition  l  that  (1)  there 
are  certain  atomic  groups  in  the  chlorophyll  which  are  set  in  strong 
vibrations  by  the  red,  and  less  strongly  by  the  more  refrangible,  rays 
of  the  spectrum,  and  (2)  it  is  these  atomic  groups  which  do  the  work 
of  assimilation  fiy  the  transformation  of  light- waves  into  chemical 
activity.  In  connection  with  (1)  we  might  mention  the  phenom- 
enon that  an  alcoholic  solution  of  chlorophyll  fluoresces  with  a  red 
light,  while  the  living  green  plant  s  does  not  fluoresce ;  that  is,  it 
does  not  emit  a  red  light,  because  the  necessary  vibrations  are 
being  transformed  into  chemical  activity.  The  coloring  substance 
chlorophyll  and  living  plasm  work  together  in  the  processes  of 
assimilation:  chlorophyll  acts  perhaps  after  the  manner  of  a 
ferment. 

The  history  of  assimilation  also  contains  the  investigations  of 
PRINGSHEIM2  which  created  considerable  interest  at  the  time. 
Pringsheim' s  hypothesis  has,  according  to  my  knowledge,  no  firm 
adherents.  The  peculiarity  of  this  hypothesis  is  the  original  con- 
ception that  the  coloring  matter  of  chlorophyll  is  only  of  physical 
importance,  not  chemical,  and  that  it  is  the  colorless  plasm  which 
is  active  in  assimilation.  According  to  Pringsheim,  chlorophyll 
regulates  the  respiration  of  oxygen  in  plants  by  the  absorption  of 
the  so-called  "chemical"  rays  (blue,  violet,  ultra-violet),  so  that 
the  activity  of  such  respiration  is  reduced  below  the  activity  of 
assimilation.  The  absorption-bands  in  the  red  therefore  cannot 
have  the  significance  mentioned  above.  The  optimum  of  assimila- 
tion, according  to  Pringsheim ; — in  agreement  with  SACHS  and 
PFEFFER, — does  not  lie  in  the  red  spectrum  but  in  the  yellow.  In 
this  matter  we  are  far  from  having  uniformity  of  opinion.  But 
we  will  for  the  time  being  adhere  to  the  opinion  expressed  above, 
which  is  based  upon  the  results  of  Engelmann's  and  Reinke's 
experiments. 


1  See  HOPPE-SEYLER,  Botanische  Zeitung  (1879),  p.  819. 

2  Sitzungsberichte  der  Berliner  Akademie,  1879. 


TISSUES  AND  SIMPLE  ORGANS.  131 

We  shall  now  further  discuss  the  process  of  assimilation. 

Each  individual  chlorophyll-grain  may  be  designated  as  a  work- 
shop of  assimilation.  The  chief  requirements  for  this  assimilation 
in  the  chlorophyll  are  the  presence  of  CO2  and  the  influence  of 
diffuse  or  direct  sunlight.  Water  is  already  present  in  the  assimi-^ 
lating  cells.  Starch '  (amyliim)  in  the  form  of  starch-grains  is,  in 
the  majority  of  instances,  the  rapidly  formed  product  of  this 
assimilation,  though  it  is  not  the  immediate  chemical  product. 
Before  solid  starch-grains  can  be  formed  there  must  be  a  product 
of  assimilation,  also  a  carbohydrate,  which  is  soluble  in  water,  as 
some  form  of  sugar ;  even  this  may  not  be  the  first  chemical  prod- 
uct. The  experimental-physiological  fact  that  there  is  a  volume 
of  oxygen  liberated  approximately  equal  to  that  of  CO2  taken  in, 
is  in  harmony  with  the  assumption  that  a  carbohydrate  is  the 
product  of  assimilation  :  1 2CO2  +  10H2O  =  24-O  +  CWH10O10 . 
According  to  recent  investigations  (ARTHUR  MEYER),  the  formation 
of  soluble  carbohydrates  (devoid  of  starch)  predominates  in  the 
chlorophyll  of  monocotyledons,  while  starch-formation  predomi- 
nates among  dicotyledons.  In  regard  to  the  immediate,  still  un- 
known, product  of  assimilation  we  may  state  that,  according  to  the 
hypothesis  of  BAYER,  CO2  and  H2O  first  unite  to  form  an  aldehyde 
(alcohol),  and  this  is  polymerized  into  a  carbohydrate  (CO2  -f- 
H2O  =  O2  +  CH2O).  LOEW  produced  a  sugar  (C6H12O6)  out  of 
the  aldehyde  formed  from  formic  acid  and  limewater. 

U  nder  favorable  circumstances  starch-formation  may  take  place 
in  a  few  minutes.  The  starch  that  is  formed  will  disappear  in 
the  dark,  also  in  the  light  in  the  absence  of  CO2 .  Among  many 
plants  the  starch  formed  during  the  day  is  carried  into  the  petiole 
of  the  leaf  and  other  tissues  during  the  night.2 

Chlorophyll-grains  as  the  workshop  of  our  most  essential  food- 
substance,  bread,  deserve  special  attention.  Our  present  scientific 
knowledge  does  not  enable  us  to  furnish  even  an  approximate 
substitute  should  the  above-described  chlorophyll  activity  cease 
altogether.  Science  does  not  even  comprehend  the  chemical 


1  As  a  note  on  microcbemistry  may  be  added.     Iodine  is  only  slightly  soluble 
in  water,  more  so  in  solution  of  KI  or  alcohol.    All  these  solutions,  more  particu- 
larly the  stronger,  serve  to  demonstrate  the  presence  of  starch  both  microscopi- 
cally and  rnacroscopically  by  a  blue  or  dark-blue  coloration  of  the  starch-grains. 

2  For  particulars  see  the  works  of  SACHS. 


132  COMPENDIUM  OF  GENERAL  BOTANY. 

methods  by  which  we  are  so  amply  supplied  with  "daily  bread." 
Much  less  is  it  capable  of  imitating  the  process  artificially. 

Chlorophyll  proves  to  be  of  great  importance  during  various- 
periods  of  chemical  activity  in  plants.1  Among  trees  with  decidu- 
ous leaves  we  see  that  the  assimilating  organs  are  destroyed  at  the 
close  of  the  vegetative  period.  Chlorophyll  itself  is,  however,  not 
simply  lost;  in  the  autumn  before  the  leaves  begin  to  fall  the 
most  valuable  mineral  constituents  (kalium,  phosphoric  acid)  pass 
into  the  enduring  portions  of  the  plant,  to  be  again  utilized  the 
following  year ;  yellow  grains,  causing  the  autumn  coloration  of  so 
many  leaves,2  remain  in  the  cells  of  the  falling  leaves  as  a  waste 
product.  Chlorophyll-grains  therefore  undergo  decomposition. 

VII.  THE   FUNCTION   OF  AERATION. 

The  discussion  of  the  fact  that  gas-forming  and  gas-requiring 
processes  take  place  within  the  cell,  and  the  explanation  of  a  few 
simple  observations  associated  therewith,  will  enable  us  to  under- 
stand correctly  the  structural  arrangements  to  be  discussed  below. 

If  one  considers  the  fact  that  air  never  occurs  in  the  form  of 
bubbles  within  the  active  living  cell,  and  that  the  most  important 
chemical  processes  (assimilation  of  atmospheric  COa  with  liberation 
of  oxygen,  and  true  respiration  with  liberation  of  CO2)  take  place 
in  the  living  cells,  it  is  natural  to  conclude  that  the  active  exchange 
of  gases  which  takes  place  in  the  immediate  vicinity  of  these  cells ; 
or  in  other  words,  since  no  gas  appears  in  the  cell  in  the  form  of 
bubbles,  that  such  gas  exchange  must  take  place  between  the  cells. 
In  fact,  the  system  of  aeration  of  plants  is  intercellular,  that  is,  it 
is  situated  outside  of  the  cell.  .  • 

The  aerating  system  spreads  labyrinth-like  through  the  entire 
plant-body,  beginning  with  the  vegetative  point  at  the  apex  of  the 
stem  and  extending  to  the  root-tip ;  beginning  with  the  pith  and 
extending  radially,  it  crosses  the  wood-parenchyma,  cambium,  and 
cortex.  In  the  leaves  and  other  organs  it  extends  to  the  epidermal 
tissue,  in  the  form  of  fine  canals.  This  system  among  plants  living 
in  the  atmosphere  can  be  considered  only  as  functional  when  there 
are  suitable  anatomical  arrangements  to  permit  the  ingress  and 

1  SACHS,  Vorlesungen,  p.  384. 

3  These  bodies  are  found  in  the  cell-sap  of  those  leaves  colored  red  in  the  falL 


TISSUES  AND  SIMPLE  ORGANS.  133 

egress  of  air.  Such  anatomical  adaptation's  we  find  in  the  stomata 
(breathing-pores)  of  the  epidermis  and  in  the  lenticels  of  the  cork- 
tissue. 

It  will  not  be  found  difficult  to  understand  the  structural  dif- 
ferences between  land-plants  and  water-plants.  The  supply  of  air 
in  submerged  water-plants  is  very  limited  and  can  be  obtained  only 
from  the  water  (absorbed  air).  Plants  temporarily  or  permanently 
partially  submerged  are  also  limited  in  their  supply  of  air  as  com- 
pared with  land-plants.  Considerations  lead  us  to  the  postulate 
that  water-plants  must  carry  a  supply  of  air  with  them.  Compara- 
tive observation  reveals  the  following :  Every  palisade-cell  of  the 
leaf  of  a  land-plant  which,  for  example,  lies  in  contact  with  six 
other  cells  is  laterally  surrounded  by  six  delicate  intercellular 
canals  corresponding  to  the  six  prismatic  corners  and  edges  of  each 
cell ;  every  cubical  cell  is  enclosed  by  twelve  minute  canals,  etc. 
Otherwise,  comparing  the  intercellular 
spaces  of  land-plants  with  the  air-spaces 
occurring  in  the  leaves  and  steins  of 
water-plants  and  marsh-plants,  it  is 
noticeable  to  the  naked  eye  that  the 
latter  appear  as  cavities  and  channels. 
These  contain  a  large  supply  of  air  to 
satisfy  requirements.  Such,  in  one  re- 
spect, is  the  interpretation  of  this  phe- 
nomenon. The  relation  between  the 
magnitude  of  intercellular  spaces  and  the 
water  contained  in  the  surrounding 
medium  was  known  to  older  anatomists. 
The  accompanying  figure  (73)  shows  a 
fragment  of  the  parenchymatous  tissue 

of  a  water-plant  (from  the  leaf  of  Acorns  Calamus)  magnified 
about  three  hundred  times.'  A  positive  pressure,  due  to  the  proc- 
ess of  assimilation,1  has  been  observed  in  the  air-chambers  of  sub- 
merged green  water-plants. 

Moreover,  the  air  contained  in  submerged  and  floating  plant- 
organs  tends  to  reduce  the  specific  gravity  of  the  organs,  thus  en- 
abling them  to  float,  or  at  least  decreasing  the  tendency  to  sink. 


PFEFFER,  Physiologic,  I.  Band,  p.  85,  et  seq. 


134  COMPENDIUM  OF  GENERAL  BOTANY. 

Communication  between  the  intercellular  spaces  and  air-cham- 
bers and  the  atmosphere  is  brought  about  by  breaks  in  the  contin- 
uity of  the  epidermal  covering.  Every  breathing-pore  (stoma, 
compare  Figs.  74—79)  is  directly  opposed  to  the  function  of  the 
epidermal  system,  because  it  increases  the  loss  of  water ;  the  pores 
must  remain  open  at  least  for  a  time  in  order  to  permit  the  ingress 
of  CO2  and  the  egress  of  O.  The  closing  of  stomata  is  therefore  a 
physiological  requirement.  This  most  important  requirement  will 
be  considered  a  little  later.  The  unavoidable  loss  of  water  is  re- 
duced very  materially  by  the  facts  that  the  great  majority  of  the 
stomata  of  land-plants  are  on  the  lower  surfaces  of  the  leaves,  and 
in  protected  positions,  as,  for  example,  in  depressions;  also  by 
being  covered  with  hair-cells,  by  the  elongation  of  the  ' '  entrance, ' ' 
etc.  Comparative  anatomy  reveals  a  series  of  instances  in  which  it 
is  possible  to  know  the  habitat  of  a  given  plant  from  the  position 
and  structure  of  its  breathing-pores.  (Concerning  this  consult 
TSCHIRCH  and  other  authors.) 

Let  us  add  a  few  further  physiological  (also  teleological  in  their 
final  results)  observations  concerning  this  important  apparatus. 
Submerged  and  subterranean  organs  are,  in  general,  entirely  free 
from  stomata;  for  example,  they  never  occur  on  roots.  They 
occur  mainly  on  green  leaves  and  green  stem-organs.  It  is  also 
worthy  of  notice  that  land-plants  devoid  of  chlorophyll  (saprophytes 
and  parasites)  are  almost  uniformly  free  from  stomata  or  contain 
only  a  few.  In  bifacial  aerial  leaves  the  stomata  are,  as  a  rule,  on  the 
lower  surface,  as  has  already  been  stated ;  in  floating  leaves  they 
occur  on  the  upper  surface ;  in  centric  leaves  (not  differentiated 
into  luminous  sides  and  shade-sides)  they  are  evenly  distributed  on 
all  sides.  Their  number  varies  greatly :  from  40  to  300  per 
square  millimeter.  In  Brassica  Rapa  there  are  about  716  per 
square  millimeter.  In  leathery  leaves  they  are  smaller  and  more 
numerous ;  in  succulent  leaves  they  are  larger  and  less  numerous. 

Stomata  are  organs  especially  adapted  for  closing.  Lenticels 
take  the  place  of  stomata  when  the  epidermis  is  displaced  by  cork- 
tissue.  Investigation  in  regard  to  lenticels  shows  that  the  relative 
permeability  to  air,  at  least  in  some  plants,  is  greater  in  the  spring 
than  in  winter.  Lenticels  are  never  entirely  closed,  while  the 
stomata  may  be.  We  shall  now  consider  the  stomata  and  lenticels. 
more  in  detail. 


TISSUES  AND  SIMPLE  ORGANS.  135 

(a)  The  Structure  and  Function  of  Breathing -pores  (Stomata). 

(With  Figs.  74-79.) 

Immediately  below  the  guard-cells  there  is  a  large  intercellular 
space  called  the  air-chamber  into  which  the  intercellular  canals  of 
the  surrounding  tissue  lead.  The  space  at  v  (Fig.  74)  is  known  as 
"  front  cavity  "  (Vorhof,  entrance),  the  one  at  A  as  "  back  cavity  " 
(Hinterhof) ;  between  them  lies  the  central  passage  (Centralspalte) ; 
s  are  the  two  guard-cells ;  g  the  cuticular  joint  (Hautgelenk) ;  a 


FIG.  74.— Vertical  section  through  the  stoma  of  Amaryllis  formosissima.     Type  I. 
a,  Air-chamber.    (After  Schwendener.) 

the  air-cavity.  As  a  rule,  the  cuticle  covers  the  wall  of  the 
guard-cell  about  the  front  cavity,  and  sometimes  extends  even  to 
the  air-cavity,  as  shown  by  SCHWENDENER.  The  consideration  of 
the  mechanics  of  breathing-pores  reveals  one  of  the  most  interest- 
ing accomplishments  of  modern  teleological,  or,  better,  anatomical- 
physiological,  investigations.  We  shall  now  briefly  consider  three 
main  types  recognized  as  such  owing  to  essential  peculiarities:  1. 
Amaryllis-type,  2.'  Ifelleborus-type,  3.  Gramineous  type  (ac- 
cording to  Schwendener's  investigations). 

First  type:  Amaryllis formosissima  and  many  other  plants  of 


136 


COMPENDIUM  OF  GENERAL  BOTANY. 


widely  separated  divisions.  Volume  of  front  cavity  and  back  cav- 
ity variable;  large  guard-cells,  thin  opposing  walls.  Principle: 
a  rubber  tube  thickened  on  one  side  bends  when  pressure  is  in- 
creased in  its  interior,  while  the  thin  wall  becomes  convex.  The 
thickened  portions  (ridges  of  the  outer  and  inner  apertures)  of  the 


FIG.  75. — Surf  ace- view  of  an  open  (a)  breathing- pore  (stoma)  and  of  one  closed  (b). 
(Diagramatic.)    Illustrating  types  I  and  II. 

wall  of  the  guard- cell  which  are  nearest  each  other  cause  a  curva- 
ture of  the  guard- cells  when  the  hydrostatic  pressure  of  the  interior 
is  increased.  (By  the  presence  of  two  such  thickenings  this  cur- 
vature is  much  more  marked  than  it  would  be  if  only  one  such  ridge 
were  present.)  The  thin  areas  of  each  guard-cell  nearest  the  cen- 


FIG.  76.—IIelleborus.     Type  II. 
(After  Schwendener.) 

tral  passage  .may  permit  a  hinge-joint  movement  of  the  thickened 
ridges,  or  by  mutual  contact  they  may  form  a  better  means  of  clos- 
ing the  pore  than  do  the  thickened  ridges.  The  chief  mechanical 
change  involved  is  the  greater  expansibility  of  the  thin  distal  walls 
as  compared  with  the  thick  proximal  walls. 


TISSUES  AND  SIMPLE  ORGANS. 


137 


Second  type  :  Helleborus.  Front  cavity  immovable,  back  cav- 
ity undergoing  great  changes  in  size  and  position.  The  changes  in 
form  of  the  lumen  of  the  guard-cell  as  seen  in  cross-section  are 
such  that  in  the  non-turgescent  state  the  outline  of  cell-wall  pre- 
sents the  form  of  a  scalene  triangle  ;  in  the  turgescent  state  it  as- 
sumes more  nearly  the  form  of  an  isosceles  triangle  (see  Fig.  76). 
Chief  mechanical  change  :  hinge-  joint  movement  of  the  thin  areas 
of  the  guard-cells  near  the  central  passage  accompanied  by  a  similar 
movement  of  the  distal  wall  near  the  cuticular  joint.  The  entire 
guard-cell  may  also  become  curved.  There  will  be  no  difficulty  in 
finding  forms  intermediate  between  the  first  and  second  types. 

Third  or  Gramineous  type.  The  frequently  much-  elongated 
middle  portion  of  the  guard-cell  is  thick-  walled  and  passive.  The 
lumen  of  the  guard-  cell  in  cross-  section 
through  the  middle  presents  the  ap- 
pearance of  a  wedge  placed  transversely 
(Fig.  77).  The  movements  due  to  tur- 
gor  are  manifest  in  the  expanded  thin- 

walled    lower  ends  (subsidiary  cells)   of 
.  _       .,     ,__,. 

the  guard-cells  (Figs.  78  and  79).     The 

open  central  passage  (stoma)  is  bounded 

by  parallel  straight  lines,  formed  by  the  outline  of  the  above-men- 

tioned middle  portions  of  the  guard-cells  (Fig.  79).     The  subsid- 


G-  W-  —  Vertical  section 
through  the  storaa  of  Garex 
leporina. 


FIG.  78.— Radial  longitudinal  section  through  a  guard-cell  of  Triticum. 
(After  Schwendener.) 

iary  cells  (n)  perform  the  function  of  1 ,  a  "  membranous  hinge  ' ' 
similar  to  the  thin  cell- wall  areas  of  the  other  types ;  2,  in  a  few 
instances,  verified  by  experiment,  they  assist  in  closing  the  pores 
during  the  turgescent  state,  since  the  central  pore  has  been  observed 
to  remain  open  even  after  the  subsidiary  cells  and  guard-cells  were 
killed. 

The  exceptions  referred  to  under  type  II.  are  not  contradictory 
of  the  following  general  statement :  Increasing  turgescence  of  the 
guard- cells  is  the  force  which  causes  the  opening  of  the  pores,  and, 


138  COMPENDIUM  OF  GENERAL  BOTANY. 

conversely,  reducing  the  turgescence  of  the  guard-cells  tends  to  close 
the  pores.  Besides  this  general  statement,  a  few  special  considera- 
tions are  necessary.  It  has  been  observed  that  the  stomata  of  some 
water-plants  are  open  at  all  times  whether  the  guard-cells  are  tur- 


FIG.   79. — Surface-view  of  a  breathing-pore  of  Triticum  vulgaro.      Type  III. 

(Open.) 
(After  Schwendener.) 

gescent  or  not.  It  must  also  be  remembered,  as  has  already  been 
stated,  that  the  subsidiary  cells  in  some  cases  assist  in  closing  the 
breathing-pores.  The  opening  of  pores  is  also  influenced  by  the 
pressure  of  the  epidermal  cells. 

Why  does  the  turgor  of  the  guard- cells  increase  ?  First  of  all 
sunlight  is  the  outer  agency  which  produces  these  changes.  It  is 
evident  also  that  the  chlorophyll  of  the  guard-cells  enters  as  a  fac- 
tor in  turgor.  The  presence  of  chlorophyll  is  characteristic  of  the 
guard-cells  in  contradistinction  to  the  other  epidermal  cells.  The 
delicate  structure  or  other  peculiarities  of  the  guard-cells  are  of 
importance  in  facilitating  diosmosis  with  neighboring  epidermal 
cells  (gyrnnosperms). 

The  question  whether  warmth  has  an  effect  similar  to  that  which 
light  produces  could  not  be  satisfactorily  answered  by  SCHWENDENER, 
although  he  does  not  doubt  that  suddenly  reducing  the  temperature 
to  zero  reduces  the  turgescence  of  the  guard-cells,  while  raising  the 
temperature  increases  it. 

The  mechanism  of  the  coniferous  type  is  still  under  investiga- 
tion. 

(b)  Lenticels. 

A  knowledge  of  these  structures  presupposes  a  knowledge  of 
cork-tissue.  Lenticels  are  lense-shaped  cork-like  tissue-formations 
of  the  bark  which  have  the  peculiarity  of  always  being  traversed 


TISSUES  AND  SIMPLE  ORGAN'S. 

by  intercellular  spaces.  Little  is  known  concerning  these  organs  in 
monocotyledons.  Among  dicotyledons  and  gymnosperms  they 
originate  from  the  cork-cambium,  and  consist  either  of  entirely  su- 
berized  cells  or  sometimes  also  of  such  as  are  not  suberized ;  both 
cell- forms  contain  intercellular  spaces  radially  arranged  correspond- 
ing to  their  succcession  in  development. 

Very  frequently  lenticels  are  sufficiently  large  to  be  seen  by  the 
naked  eye,  for  example,  in  the  birch.  Their  permeability  to  air- 
has  already  been  referred  to.  Their  origin  does  not  always  coin- 
cide with  the  position  of  a  breathing-pore ;  very  frequently  lenti- 
cels are  formed  after  bark-formation  has  begun.  (KLEBAHN,  who 
continued  the  investigations  begun  by  STAHL  and  others,  has  studied 
lenticel-f or mations  more  particularly.) 

VIII.  THE   FUNCTION   OF  EOOTS. 

We  shall  discuss:  1,  the  activity  of  ordinary  or  subterranean 
roots,  and  2,  that  of  aerial  roots.  Their  internal  anatomical  struc- 
ture (the  transit-cells  in  the  protective  sheath,  etc.)  has  already 
been  discussed. 

(a)  Subterranean  Roots. 

From  the  fact  that  the  absorption  of  food  is  to  be  accomplished 
by  closed  cells  it  is  easy  to  comprehend  that  such  food-substance 
must  be  in  a  soluble  (capable  of  osmosis)  form.  Water  and  watery 
solutions  of  mineral  substances  whose  chemical  composition  and 
nature  will  be  considered  elsewhere  are  of  special  importance. 
The  portion  of  the  root  which  serves  the  purpose  of  taking  up  the 
food- substances  is  comparatively  small;  it  is  located  behind  the 
root-cap  and  is  considerably  increased  in  surface  by  its  numerous 
root-hairs.  In  young  roots  the  portion  bearing  the  root- hairs 
comprises,  in  general,  the  greater  portion  of  the  entire  root-surface 
exclusive  of  the  very  tip,  in  older  roots  only  the  portion  immedi- 
ately behind  the  root-tip  (see  Fig.  80). 

Transverse  septa  are  wholly  wanting  in  the  root-hairs,  branch- 
ing rarely  occurs,  so  that  they  represent  long  papillose  outgrowths 
of  the  epidermal  cells  (Fig.  81).  The  absence  of  transverse 
septa,  the  thinness  of  the  cell-wall,  the  irregular  curvatures — all 
serve  the  specific  purposes  of  root-hairs,  namely,  to  bring  them  in. 


140 


COMPENDIUM  OF  GENERAL  BOTANY. 


contact  with  water  and  particles  of  soil,  to  enable  them  to  take  up 
and  conduct  food-substances  in  solution.  Other  substances  not 
soluble  in  water  are  rendered  capable  of  being 
taken  up  by  the  root-hairs.  Some  mineral  sub- 
stances are  made  soluble  by  a  secretion  of  the  root 
itself,  perhaps  an  organic  acid.  According  to 
SACHS,  this  may  be  demonstrated  by  means  of  a 
polished  marble  plate,  osteolith-  or  dolomite-plate, 
upon  which  growing  roots  produce  figures  of 
corrosion.  Blue  litmus  paper  is  turned  red  by 
this  excretion  of  the  roots.  The  activity  of  the 
root-hairs  also  reduces  or  entirely  removes  certain 
salts  from  the  soil,  as  lime-salts,  phosphates,  and 
compounds  of  ammonia.  Besides  the  organic  acid 
referred  to,  roots  also  secrete  COa . 

In  plants  devoid  of  roots  the  soluble  food-sub- 
stances are  taken  up  by  the  rhizoids,  hair-like 
structures  met  with  among  the  prothallia  of  ferns, 
and  among  the  lichens  and  mosses.  In  Marchantia 
these  hair-like  rhizoids  possess  peculiar  elevated 
80  -  A  A  thickenings  of  the  cell- wall  which  project  inward ; 
they  have  perhaps  a  mechanical  function,  namely, 


PIG. 


young     seedling 

with  particles  01  .  /.  ,-, 

soil   adhering  to  to  prevent  collapse  01  tlie  cells. 

the  root-hairs.  B, 

The    same    with 

soil- pa  r tides 

washed  away. 

•(After      Sachs,     from 
Frank.) 


(b)  Aerial  Roots. 

In  the  plants  of  moist  warm  climates — a  con- 
dition artificially  produced  in  our  greenhouses — 
roots  very  frequently  develop  from  aerial  organs.  Such  roots 
may  subsequently  enter  the  soil,  in  which  case  the  subterranean 
portion  performs  the  function  of  an  ordinary  root;  or  they 
may  remain  permanently  suspended  in  the  air,  in  which  case 
they  are  specially  organized  to  serve  as  aerial  organs  (Aroideot, 
epiphytic  orchids).  In  the  anatomy  of  true  aerial  roots  there 
is  found  just  outside  the  normal  root- cortex  a  covering  of 
several  cell-layers  in  thickness  called  the  velamen.  The  cells 
of  this  layer  are  filled  with  air  and  the  walls  contain  delicate 
spiral  or  reticular  thickenings.  The  special  function  of  this  cell- 
layer  is  to  absorb  water-vapor.  Between  the  velamen  and  the 
cortex  there  is  a  layer  of  cells  which  is  known  as  ' '  endoderm ; ' ' 


TISSUES  AND  SIMPLE  ORGANS,  141 

this  name  suggests  its  similarity  to  the  protective  sheath  (endoderm) 
of  ordinary  roots.  In  it  are  found  passages  to  the  internal  paren- 
chyma (LEITGEB)  '  which  no  doubt  serve  to  conduct  moisture  to  the 


FIG.  81. — Cross-section  of  a  root  with  root-hairs. 
(After  Frank.) 

interior.  The  outermost  cells  of  the  velamen  may  develop  hair- 
like  structures,  especially  when  the  growing  root  lies  in  contact 
with  a  solid  moist  body. 

IX.  THE   APPKOPKIATION   OF   ASSIMILATED   FOOD- 
SUBSTANCES. 

In  order  to  form  a  correct  conception  of  the  processes  of  nutri- 
tion which  are  about  to  be  considered  it  is  necessary  to  have  a  clear 
understanding  of  carbon-assimilation  (see  pp.  128  et  seq.}.  It  is 
true  that  the  mass  of  solid  food-substances  and  increase  in  the 
weight  of  plants  can  be  traced  to  the  disintegration  of  atmos- 
pheric CO2  by  the  green  organs ;  but  plant-life  in  its  various  con- 
ditions and  conformations  presents  a  series  of  phenomena  which 
occur  as  regularly  as  the  process  of  assimilation,  and  which  teach  us 
that  the  appropriation  of  food-substances  already  assimilated  is  an 


This  investigator  (1864)  made  a  special  study  of  the  aerial  roots  of  orchids. 


142 


COMPENDIUM  OF  GENERAL  BOTANY. 


essential  part  of  plant -nutrition.  Of  the  four  important  conditions 
coming  under  this  heading  three  are  widely  distributed  and  shall 
receive  our  immediate  attention. 


(a)   Condition  of  Seeds  before  the  Seginmng  of  Assimilation. 

The  undeveloped  embryo,  which,  when  mature,  becomes  sepa- 
rated from  the  mother-plant,  receives  a  greater  or  lesser  supply  of 

stored  food-substances  during  its 
attachment  to  the  mother-plant, 
which  serve  as  the  initial  food- 
supply  during  germination.  This 
is  very  marked  in  our  cereals.  The 
mass  of  the  grain  consists  of  stored 
food-substance,  the  starch-bearing 
endospermous  tissue  y  1  the  small 
embryo  (see  Fig.  82)  is  situated  at 
one  side.  We  may  obtain  a  better 
summary  of  various  seed-  structures 
by  separating  them  as  to  their  com- 
position and  mode  of  appropriating 
or  reabsorbing  the  stored  food-sub- 

FIG.    82.  —  Longitudinal   median  sec-   stance. 

tion  through  the  seed  of  Zea  Mays.  -,      m  i 

*,  Epidermal  layer  ;  n,  point  of  attachment  1-     1«*  embryo  £08868868  a  Spe- 

of  the  style  ;   fs,  base  of  the  ovary  •  eo      •   -i    n    i     1*111  *i  fee.          J.T 

compact  and  ew  less  compact"  portion  of    Cial  flat  shield-like    Organ  ("  SCUtel- 

the  endosperm  ;  sc  and  ss,  scutellum  (ab-    ,          .  ,N        ,  ,.          ..         ..     . 

sorbing  organ)  with  epider  in  is  e  ;  fc,  young    mm      )  WuOSe    junction  it    IS    to    ab- 

leaves  ;    st,  first  iiiternode  of  the  stem  ; 

w,  main  root  ;  w',  lateral  roots  springing    SQrb  the  f  OOd-SllbstanCCS  of    the  en- 

from  the  stem  ;  tvs,  root-sheath.    (After 

Sachs-)  dosperm.      This   organ    sometimes 

develops  papillse-like  projections,  which  penetrate  the  endosperm- 
tissue  in  order  to  facilitate  the  absorption  of  the  food-material 
(grasses;  see  Fig.  82). 

2.  Among  certain  palms  there  is  a  wart-like  apical  portion  of 
the  cotyledon  which  serves  to  absorb  the  food-material. 

3.  The  cotyledons  themselves  are  very  frequently  the  bearers 
of   the  reserve  food-  substance  ;    examples  :    Quercus-seeds,   beans, 
peas,  lentils,  etc.     In  the  beginning  the  cotyledons  are  fleshy,  sub- 
sequently they  shrink,  as  the  food-material  is  removed  during  germi- 


sc 


1  Iu  this  case  the  expression  "  seed-albumen  "  is  chemically  incorrect,  since  the 
substance  consists  essentially  of  a  carbohydrate. 


TISSUES  AND  SIMPLE  ORGANS. 


143 


nation  (Fig.  83).  Strictly  considered,  this  is  really  a  case  which 
serves  for  the  circulation  and  utilization  of  the  assimilated  food- 
substances  in  one  and  the  same  plant,  and  not  for  the  appropriation 
of  food- substances  from  the  outside. 

4.  The  cotyledons  at  first  serve  as  organs  to  absorb  the  endo- 
sperm, and  subsequently  become  organs  of  assimilation  (see  Fig. 
84,  which  represents  a  seedling  of  Pinus  Pineal) 


FIG.  83.— Bean-seedling. 
(After  Krass  and  Landois.) 


FIG.  84.— Seedling  of  Pinus  Pinea. 

w  and  mv,  Roots  :  c,  cotyledons  ;  he,  hypocoty- 
ledonous  stem  (radicle);  s,  outer  seed-coat; 
r,  inner  seed-coat.  (After  Berthold  and  Lan- 
dois.) 


5.  The  cotyledons  contain  some  food-material  and  begin  the 
function  of  assimilation  as  soon  as  the  reserve  food  is  assimilated. 
The  endosperm  is  wanting.  The  cotyledons  soon  become  green 
(Oruciferce).  This  case,  like  number  3,  is  introduced  for  the  sake 
of  completeness. 


(b)  Nutrition  of  Saprophytes  and  Parasites. 

The  term  ' '  parasite  ' '  in  itself  indicates  that  the  organisms 
referred  to  require  an  organic  substratum  upon  which  to  live.  The 
assimilation  of  food-substances  prepared  by  life-processes  is  common 


144  COMPENDIUM  OF  GENERAL  BOTANY. 

to  both  saprophytes  and  parasites.  If  the  food-supplying  organism 
is  alive  and  injuriously  affected  by  such  a  relation,  it  is  recognized 
as  parasitism.  Vegetable  parasites  are  either  endophytic  or  epi- 
phytic, that  is,  either  growing  within  the  plant  or  attached  to  the 
outer  surface.  If  the  organic  substances  belong  to  dead  organisms, 
the  organisms  living  upon  them  and  taking  nourishment  from 
them  are  known  as  saprophytes.  Theoretically  these  groups  may 
be  clearly  separated,  but  actual  observation  teaches  that  the  two 
modes  of  life-activity  may  become  interchanged  or  may  occur  side 
by  side. 

Fungi  are  entirely  dependent  upon  organic  food,  since  they  con- 
tain no  chlorophyll.  In  the  numerous  fungi  which  infect  living 
plants,  but  which  can  only  reach  their  maximum  development  on 
dead  plants,  parasitism  and  saprophytism  seem  to  alternate. 

The  few  phanerogams  devoid  of  chlorophyll  are  also  dependent 
upon  assimilated  or  organic  food ;  for  example,  the  orchid  Epipo- 
gon  Gmelini  is  a  saprophyte,  Cuscuta  is  a  parasite ;  Monotropa  is 
said  to  be  both  parasitic  and  saprophytic.  Viscum  album,  the 
well-known  mistletoe,  is  evidently  parasitic,  although  its  green 
leaves  have  the  power  of  assimilation ;  Neottia  nidus  avis  is  a  sap- 
rophyte and  has  some  power  of  assimilation  owing  to  the  chloro- 
phyll in  the  reduced  scaly  leaves. 

Parasitic  phanerogams  present  remarkable  anatomical  arrange- 
ments, which  enable  them  to  take  up  assimilated  food- substances. 
The  details  of  this  adaptive  arrangement  were  studied  by  SOLMS- 
LAUBACH,  and  L.  KOCH.  There  are  three  characteristic  parts  to 
the  organ  which  serves  to  absorb  the  food-substances;  namely, 
the  haustorium,  the  sucker,  and  the  absorbing -cells.  These  are 
shown  in  figure  85,  A  and  B.  B  represents  the  absorbing 
cells,  s  the  sucker  somewhat  magnified ;  w  is  the  root  of  the  host- 
plant. 

In  regard  to  the  parasitic  fungi  which  have  the  power  of  pene- 
trating cell-walls,  it  is  to  be  noted  that  this  phenomenon  is  associated 
with  the  excretion  of  ferments  having  the  property  of  dissolving 
suberized  as  w^ell  as  unsuberized  cell- walls.  To  the  Schizomycetes 
(bacteria)  especially,  various  fermentative  activities  are  ascribed,  not 
only  for  the  purpose  of  dissolving  cell-membranes  but  also  for  dis- 
solving albuminous  substances.  The  fact  that  chlorophyll-bearing 
plants  occur  parasitically  on  rhizomes  and  roots  of  other  plants 


TISSUES  AND  SIMPLE  ORGANS. 


145 


very  probably  indicates  that  they  are  partially  dependent  upon  a 
nitrogenous  food-supply. 1 

The  following  substances  serve  as  food  for  bacteria  and  moulds : 
the   carbohydrates,    various    organic    acids,    glycerin,    albuminous. 


FIG.  85. — Haustorium  of  TJiesium  pratense. 
(After  Solms-Laubach.) 

substances,  peptone,  leucin  and  asparagin.  These  substances  and 
many  others  were  used  by  PASTEUR,  and  NAGELI  in  numerous 
culture-experiments. 

(<?)  Symbiosis. 

Externally  symbiosis  resembles  parasitism  in  that  it  represents 
the  organic  union  of  one  plant  with  another.  On  closer  examina- 
tion, however,  we  notice  a  marked  difference.  In  the  definition 
of  parasitism  it  was  stated  that  the  host-plant  was  in  some  way 
injuriously  affected.  In  symbiosis  two  plants  live  together  as  in 
parasitism,  but  they  mutually  assist  each  other  in  their  life  func- 
tions, especially  in  nutrition.  The  term  symbiosis  was  introduced 
by  DE  BARY  in  his  work  entitled  "  Die  Erscheinung  der  Sym- 
biose,"  published  in  1879. 

The  most  important  example  is  met  with  in  liehe-ns  (Figs.  86- 
88),  the  true  nature  of  which  was  made  known  by  SCHWENDENER'S 
epoch-making  researches  (1860-1870).  Other  important  researches 
in  the  same  line  were  carried  on  by  BORNET,  DE  BARY,  STAHL> 


1  PPEFFER,  Pflanzenphysiologie. 


146 


COMPENDIUM  OF  GENERAL  BOTANY. 


REINKE,  and  others,  some  before  and  some  after  Scliwendener. 
Lichens  predominate  in  the  colder  climates,  where  they  frequently 
cover  large  areas  of  soil ;  in  our  zone  they  occur  on  trees,  rocks, 
etc.,  in  the  form  of  crustaceous,  foliaceous,  or  fruticose  growths. 
The  chlorophyll -bearing  algae  ("  gonidia  ")  perforni  the  assimilat- 
ing function  of  this  consortium,  while  the  fungus,  which  usually 
constitutes  the  greater  bulk  of  the  lichen-body,  serves  to  take 
up  water  and  watery  solutions  and  to  form  the  attachment  to  the 
substratum  (by  means  of  rhizoids),  and  has  also  the  function  of 
sexual  reproduction.1  REES  and  STAHL  have  observed  the  develop- 
ment of  the  thallus  of  a  lichen  by  the  artificial  synthesis  of  an  alga 


FIG.  S7.—Cladoma  cornucopioides. 
(After  Berthold  and  Landois.) 


FIG.  86.  — Sticta  fuliginosa. 

(X500.)    (After  Sachs.) 


FIG.  88. — Parmelia  parietma. 

(After  Krass  and  Landois.) 


and  a  fungus.  Fig.  86  shows  the  anatomical  structure  of  the 
thallus  of  a  foliaceous  lichen  as  seen  in  cross-section :  <?,  upper 
cortical  layer ;  u,  lower  cortical  layer ;  ?*,  rhizoids ;  m,  medullary 
layer  ;  ^,  algal  layer  (gonidial). 

Again  and  again  a  tendency  manifests  itself  among  certain  in- 
vestigators to  point  out  ' '  unsuitable ' '  conditions  and  relations  in 


1  Lichen-spores  are  very  probably  not  sexual  products.     STAHL'S  observations 
on  Gollema  microphyllum  have  not  yet  been  verified. — TRANS. 


TISSUES  AND  SIMPLE  ORGANS. 


147 


plant-life,  as,  for  example,  plant- diseases  produced  by  parasites. 
There  are  also  minds  which  cannot  understand  how  such  pathological 
changes  can  be  harmonized  with  the  original  perfection  of  the 
vegetable  creation.  Let  such  direct  their  attention  to  the  above 
facts  of  symbiosis,  which  show  that  conditions  which  at  first  sight 
resemble  parasitism  are  in  fact  beneficial  to  both  plants.  Epiphvtic 
and  endophytic  association  of  plants  does  not  in  all  instances  bear 
the  stamp  of  the  pathological  or  unsuitable.  Furthermore,  it  is  in 
perfect  harmony  with  the  Christian  conception  of  creation  that  the 
arrangements  in  nature  no  longer  possess  their  highest  perfection. 
The  injurious  and  pathological  has  no  doubt  made  its  appearance 
secondarily,  and  was  not  originally  introduced-  The  teleological 
view  of  nature  is  not  obscured  by  the  erroneous  conception  of  para- 
sitic phenomena  in  the  plant-kingdom,  nor  by  the  narrow  affirma- 
tion that  diseases  of  man  cannot  be  harmonized  with  the  doctrine 
of  the  omnipotence  of  an  all-wise  Being. 

There  is  a  very  remarkable  phenomenon  of  general  occurrence, 
wThich  is  doubtless  a  form  of  symbiosis,  the  more  correct  knowledge 
of  which  we  owe  to  various  investigators,  especially  to  FRANK. 
This  is  the  mycorhiza  (fungus- 
root)  of  certain  trees.  In  all 
climates  the  terminal  root- por- 
tions of  certain  forest  trees,  as 
C//j »tlif<>rce*  Betiilacem,  Conif- 
er<i<\  are  covered  with  hyphse 
of  some  fungus  ("  ectotrophic 
mycorhiza ' ')  which  perform  the 
function  of  root-hairs  and  also 
bike  up  food-substances  from 
the  soil.  The  biological  inter- 
relation has  as  yet  not  been  ex- 
plained very  satisfactorily.  In 

reference  to   Fig.  89  it   should  Fm    89._Ro0t_ttp  of    Carpinus  Betulus 
be  stated  that  higher  magnifica- 
tions of  a  longitudinal  section 
shows  that  the  hyphse  of  the  fungus  (m,  s,  m)  actually  surround  the 
epidermal  cells  of  the  root. 

Here  also  must  be  added  the  ' '  endotrophic  ' '  mycorhiza  of  the 
Ericacem,  etc. ,  as  well  as  the  symbiosis  in  the  swelling  of  the  roots 


with  mycorhiza. 
(After  Frank.) 


148  COMPENDIUM  OF  GENERAL  BOTANY. 

of  Elceagnacece  and  Myricacece,  and  finally  the  well-known  root- 
tubercles  of  Leguminosce.  The  latter  are  neo-formations  from  the 
root  itself  caused  l>y  and  inhabited  by  fungi  (bacteria,  rhizobia).  The 
formation  of  these  tubercles  can  be  prevented  only  by  previously 
sterilizing  the  soil,  for  example,  at  100°  C.  moist  heat  or  at  higher 
temperature  of  dry  heat ;  from  this  we  conclude  that  the  tubercle  - 
producing  organisms  are  generally  distributed  in  the  soil.  At 
certain  times,  such  as  near  the  close  of  the  vegetative  period  or 
during  lack  of  moisture,  the  leguminous  plant  digests  and  assimi- 
lates the  greater  part  of  the  infecting  bacteria,  while  a  small  number 
escape  from  the  decaying  tubercles  and  subsequently  enter  other 
roots. 1 

According  to  the  observations  of  BECCARI,  FRITZ  MULLER, 
DELPINO,  and  A.  F.  W.  SCHIMPER,  plants  and  animals  may  associ- 
ate in  symbiotic  relations.  The  investigators  mentioned  made 
observations  on  the  reciprocal  relations  between  ants  and  plants  in 
tropical  America,  communicated  by  Schimper  in  1888.  Strictly 
speaking,  this  subject  does  not  come  within  the  scope  of  the  present 
work,  yet  it  has  some  bearing  on  true  symbiosis,  and  for  that  reason 
will  be  briefly  treated.  A  certain  species  of  ant  lives  upon  and 
obtains  its  food  from  the  branches  of  a  tree  (Cecropia]\  in  return 
the  ants  protect  the  tree  from  the  injurious  and  destructive  attacks 
of  another  species  of  ant.  These  "  myrmecophilous  "  trees  have 
a  hollow  stem  transversely  divided  into  chambers;  each  chamber 
contains  an  opening  leading  to  the  exterior  through  which  the  ants, 
move  in  and  out.  This  opening  is  made  by  the  protecting  ants 
which  eat  away  a  thin  lateral  septum.  On  the  lower  surface  of 
the  petiole  there  are  small  pear-shaped  bodies  rich  in  albumen  and 
fatty  oil.  These  drop  off  very  easily,  but  others  are  continually 
formed  and  serve  as  food  for  the  protecting  ants.2 

(d)  Insectivorous  Plants. 

We  have  seen  that  plants  take  up  assimilated  food,  that  roots 
excrete  acid  for  the  purpose  of  dissolving  particles  of  soil ;  to  these 


1  The  literature  on  this  subject  is  very  voluminous.     FRANK  in  his  Lelirbuch 
der  Botauik  (1893)  gives  the  more  important  conclusions,  also  the  more  important 
citations,  of  the  literature. 

2  Various  myrmecophilous  plant-species  with  different  species  of  protecting  ants 
have  also  been  observed  and  collected  in  South  America  by  Dr.  H.  H.  Rusby. — 
TRANS. 


TISSUES  AND  SIMPLE  ORGANS. 


149 


and  similar  phenomena  we  shall  add  another  which  has  been  ob- 
served in  about  fifteen  species  of  plants,  that  is,  the  digestion  of 
animal  substance  by  plants.  The  most  interesting  features  of  these 
4 '  insectivorous  ' '  plants  are  the  specific  arrangements  for  the  cap- 
ture of  living  insects. 

Our  indigenous  genus  Drosera  shall  first  be  cited  as  a  typical 
example  (Fig.  90).  Small  insects  adhere  to  the  sticky  substance 
excreted  from  the  glandular  en- 
largements of  the  "  tentacles  " 
(trichomes)  covering  the  margin 
and  the  entire  upper  surface  of 
the  leaf.  The  pressure  of  the 
insect  acts  as  a-  stimulus  which  is 
conveyed  from  tentacle  to  ten- 
tacle, until  finally  all  the  tentacles 
incline  toward  the  middle  of  the 
leaf  (Fig.  90,  e).  The  insect  dies 
and  the  albuminoid  portion  is  dis- 
solved by  a  copious  secretion  from 
the  many -celled  glandular  struc- 
tures which  acts  similar  to  the 
gastric  ferment  pepsin.1  The 
chitinous  skeleton  remains  un- 
changed and  is  finally  discarded. 
The  dissolved  substances  are 
taken  up  by  the  leaf,  and  the 
trichomes  resume  their  normal  ir- 
ritable position.  ^  In  Dionaea  FIG  ^.- 
the  glandular  hairs  secrete  the  (After  Krass  and 
ferment  and  the  acid  only  after  they  have  been  irritated.  In  the 
leaves  of  Nepenthus  (Madagascar)  the  ferment  is  secreted  without 
any  mechanical  stimulus,  while  the  secretion  of  acid  is  due  to  the 
presence  of  a  chemical  stimulus.  In  the  case  of  Drosera  it  remains 
a  question  whether  or  not  the  ferment  is  secreted  without  the 
presence  of  a  stimulus.  It  is  believed  that  the  appropriation  of 
animal  food  by  some  insectivorous  plants  (Dionaea  and  Aldrovandd) 


1  According  to  recent  investigations  this  digestive  ferment  is  secreted  by  bac- 
teria living  011  the  plant. — TRANS. 


150  COMPENDIUM  OF  GENERAL  BOTANY. 

is  only  facultative.1  Conclusive  results  have  not  yet  been  obtained 
in  regard  to  other  species.  (It  must  also  be  borne  in  mind  that 
there  are  many  investigators  who  deny  that  green  plants  can  as- 
similate animal  food. — TRANS.) 


X.  THE  STOKING  AND  FUNCTION  OF  KESEKYE 
MATEEIAL. 

(a)  Storing  of  Water. 

The  epidermal  water- supply  ing  system  ("aqueous  tissue") 
acquires  such  thickness  in  some  plants  (Piperacece,  Bromeliacece) 
that  it  evidently  not  only  serves  as  a  water-bearing  covering,  but 
also  as  a  reservoir  for  water.  Some  internal  aqueous  tissues  also 
belong  here.  For  example,  in  the  leaf  of  some  species  of  Alee  an 
internal  water-bearing  tissue  is  enclosed  by  the  assimilating  tissue. 
In  such  orchids  as  are  especially  adapted  to  withstand  great  dryness 
isolated  water-cells  (idioplasts)  are  found  distributed  through  the 
assimilating  tissue.  These  reservoir-tracheids  have  fibrous  thicken- 
ings of  the  wall  which  prevent  the  collapse  which  would  be  caused 
by  the  excessive  hydrostatic  pressure  of  the  surrounding  cells. 
One  of  the  typically  xerophilous  plants,  Mesembryanthemum 
crystallium,  is  supplied  with  enlarged  epidermal  cells  occurring  in 
the  leaf  and  petiole,  which  are  filled  with  water.  During  excessive 
dryness  the  plant  receives  its  supply  of  water  from  these  cells.  In. 
some  extreme  cases  of  the  development  of  water-tissue  the  water 
contains  a  large  percentage  of  saline  substances  in  solution  which 
reduce  transpiration.  In  xerophilous  grasses  (Eragrostis,  Cy mo- 
don)  it  has  been  observed  that  the  leaves  become  alternately  broader 
or  narrower  according  to  the  amount  of  water  present.  This  is 
due  to  the  fact  that  the  lamellae  of  the  water-tissue  alternate  with 
the  lamellae  of  the  assimilating  tissue ;  the  former  shrink  on  the 
loss  of  water,  thereby  reducing  the  width  of  the  leaf.  In  still  other 
cases  there  is  a  folding  and  unfolding  due  to  similar  changes  within 
the  so-called  "hinge-cells"  (TSCHIECH). 


,  Uber  fleischfressende  Pflanzen,  etc.,  Landwirtschaftlicbe   Jahr- 
bttcher,  1877. 


TISSUES  AND  SIMPLE  ORGANS. 


151 


(5)  The  Storing  of  Starch  and  Other  Food-substances,  Especially 
the  Albuminous  Substances. 

Entire  organs  and  complexes  of  organs,  even  entire  plants, 
have  at  times  the  character  of  reservoirs  for  reserve  materials. 
Parenchyma,  medullary  rays,  cortical  tissue,  and  especially  the 
woody  tissue  of  trees  during  winter,  may  serve  as  storage-tissue. 

Sometimes  nitrogenous  (especially  albuminous)  and  non-nitro- 
genous (carbohydrates,  fatty  oils)  substances  occur  in  one  and  the 
same  tissue.  Protoplasm  and  starch 
occur  in  the  potato,  protoplasm  and 
dissolved  sugar  in  the  beet,  protein- 
granules  (albumen)  and  starch  in  the 
cotyledons  of  beans,  peas,  and  lentils. 
In  other  cases  the  reserve  carbo- 
hydrates occur  in  the  form  of  cellu- 
lose :  thick-walled  cells  with  numer- 


FIG.  91. — Section  of  the  peripheral 

portion  of  a  grain  of  wheat. 
5,  Seed-coat;  kl,  gluten-bearing   layer;   z, 

starch-bearing  endosperm-cells.    (X  300.) 

(After  Haberlaudt.) 


FIG.  92. 

A,  Iris-seed  in  tangential  longitudinal  sec- 
tion. B.  Cross-section  of  the  same  in  the 
direction  ab.  C,  Seed  of  Anethum  Sova 
in  cross-section.  The  arrangement  of 
the  endosperm-cells  is  indicated  by  the 
lines.  (Schematic.)  (After  Haberlandt.) 


ous  pores  form  the  storage-tissue  of  Fritillaria  imperialis,  of  the 
date-palm,  of  Phytelaphas  macrocarpa  ("  vegetable  ivory"),  and 
of  Coffea  arabica.  In  most  of  our  grasses  albumen  and  carbo- 
hydrates occur  separately  in  different  tissues ;  the  cereals  contain  a 
peripheral  layer  bearing  protein-grains  (gluten-bearing  layer),  while 
the  mass  of  the  storage-tissue  contains  the  starch  and  a  small  amount 
of  protein  (Fig.  91). 

The  storage-cells  are  sometimes  strikingly  arranged  in  straight 
rows  or  in  curves.  Such  arrangement  may  be  dependent  upon 
mechanical  or  physiological  requirements.  The  mechanical  prin- 


COMPENDIUM  OF  GENERAL  BOTANY. 

ciple  is  very  evident  from  the  fact  that  the  cell- rows  are  arranged 
along  the  lines  of  greatest  tension  (Fig.  92). 

"When  the  seed  of  Anethum  Sova  (Fig.  92,  0)  swells  during  ger- 
mination, it  increases  considerably  (28  per  cent)  in  the  diameter  ab\ 
in  this  diameter  there  is  also  a  maximum  pressure  of  the  soil ;  the 
diameter  in  the  horizontal  direction  increases  only  11  per  cent.  The 
tangential-longitudinal  section  of  Iris-seed  shows  the  mechanical 
curves.  In  cross-section  we  see  these  lines  radiate  from  the  embryo, 
where  they  are  evidently  of  physiological,  not  mechanical,  signifi- 
cance. HABERLANDT  has  made  a  special  study  of  storage-tissues  and 
the  mechanical  and  physiological  arrangements  just  referred  to.1 
In  mytreatment  of  this  subject  I  have  adhered  to  Haberlandt's 
interpretations. 

XI.  SECRETION. 

The  products  of  plant-metabolism  which  cannot  be  further  uti- 
lized in  the  plant-economy r,  and  which  do  not  form  a  part  of  the 
cell  (as,  for  example,  the  cell- wall),  are,  in  general,  designated  as 
secretions.  In  this  collective  noun  I  include  secretions  in  the  nar- 
rower sense  as  well  as  excretions* 

"We  may  designate  all  those  products  formed  from  special  or- 
gans— the  organs  of  secretion,  or  glands — as  secretions,  in  the  nar- 
rower sense.  ' '  Excretion  ' '  is  not  the  product  of  a  specific  organ ; 
the  waste  material  collects  in  certain  cells  not  united  to  form  a  dis- 
tinct structure,  while  true  secretion  is  invariably  associated  with  an 
apparatus  marked  by  specific  anatomical  peculiarities  (HABER- 
LANDT). 

Our  imperfect  chemical  knowledge  of  the  subject  does  not  per- 
ihit  us  to  give  any  detailed  description  of  the  phenomena  under 
consideration.  We  shall  briefly  consider  secretion  in  general. 

The  saccharine  solution  in  the  nectaries  of  flowers,  the  resin  of 
conifers,  the  etherial  oils,  many  of  the  formations  of  calcium  oxa- 
late,  the  tannin  in  many  cells,  and  the  water  of  transpiration  are  all 
products  not  required  in  further  metabolic  processes. 

We  can  see  the  utility  of  many  of  these  substances  and  their 
great  importance  in  plant-life ;  therefore  secretion  does  not  imply 
a  useless  product.  It  is  also  evident  that  a  substance,  as  sugar, 


1  HABERLANDT.  Physiologische  Pflanzeu-Anatomie. 
'  Ibid.  p.  320. 


TISSUES  AND  SIMPLE  ORGANS.  153 

may  be  a  secretion  in  one  part  of  the  plant,  and  in  another  part  it 
may  be  a  plastic  substance. 

Concerning  the  physiological  significance  of  many  secretions,  it 
may  be  mentioned  that  the  sweet  secretions  of  the  nectaries  and 
the  etherial  oils  are  of  importance  in  cross-fertilization,  due  to  the 
attraction  they  have  for  the  appropriate  pollen -bearing  insects. 
The  sticky  secretion  of  the  stigma  serves  to  retain  the  pollen  as 
well  as  to  aid  in  the  formation  of  the  pollen-tube.  Resinous  secre- 
tions serve  to  cover  and  protect  injured  parts.  Certain  sticky  se- 
cretions from  superficial  glands  serve  to  keep  off  injurious  crawling 
insects  (KEENER).  According  to  STAHL,'  the  acicular  bundles  of 
calcium  oxalate  which  occur  so  frequently  in  various  tissues  serve 
as  a  protection  against  animals,  particularly  snails,  that  attempt  to 
feed  upon  the  plants ;  tannin  serves  a  similar  purpose.  Sticky  resin- 
ous secretions  sometimes  unite  the  bud-scales  (in  winter)  and  protect 
them  against  moisture  and  decay.  Waxy  coatings  (example  of  use- 
ful excretion)  reduce  the  transpiration  and  evaporation  of  moisture. 
The  secretions  of  insectivorous  plants  must  also  be  included  here. 

The  translucent  spots  on  many  leaves  frequently  indicate  the 
location  of  glandular  structures,  mostly  internal  glands  as  distin- 
guished from  external  glands;  two  examples  of  the  latter  are 
shown  in  Fig.  93.  Besides  the  external  and  internal  glands,  we 
shall  refer  more  particularly  to  the  duct-like  secreting  organs. 
The  resin- ducts  of  conifers  (they  occur  in  the  wood,  bark,  and 
leaves),  the  oil-ducts  of  the  Umbelliferce,  and  the  resin-ducts  of 
Cycas  may  be  mentioned  as  the  more  important  examples. 

Of  the  c '  excretions  ' '  there  are  receptacles  containing  a  mucous 
substance ;  again  we  find  cells  more  or  less  filled  with  resin  or  oil, 
receptacles  bearing  tannin  or  crystals,  also  the  so-called  "  cysto- 
liths ' '  occurring  in  Ficus.  Receptacles  for  rnucus  occur  in  the 
Malvaceae.  In  the  Apoidece,  Composite,  and  Convolvulacece  we 
find  resin- bearing  tubes  resembling  the  laticif  erous  tubes  (DE  BARY). 

In  agreement  with  DE  BARY  2  I  wish  to  emphasize  that  not  all 
secreting  organs  are  the  result  of  cell- fusion ;  many  of  them  are 
intercellular  ducts  and  chambers.  If  they  are  formed  by  the 
crowding  apart  of  cells,  they  are  said  to  be  formed  according  to  the 
•"  schizogenous  "  method.  Example:  the  resin-ducts  of  conifers. 

1  Pflanzeu  und  Scbneckeu,  1888. 

2  Comparative  Anatomy. 


154 


COMPENDIUM  OF  GENERAL  BOTANY. 


If  they  are  the  result  of  the  solution  or  disorganization  of  cells,  they 
are  said  to  be  formed  by  the  ' '  lysigenous ' '  method,  or  ' '  rhexige- 


FIG.  94.— Kesin-duct  in  the  leaf  of 
*  Pinus  silvestris.     (AfterHaberlandt.) 

PIG.  93.— External  glands  :  A,  from  the  peti-    *.  Secreting  cells ;  *,  protective  sheath 
ole  of  Pelargonium  zonale;  B,  from  the  leaf 
of  Ribes  nigrum. 

a,  6,  and  c,  Successive  stages  of  development ; 
s,  secretion  ;  v,  receptacle  for  the  secretion  ;  2,  se- 
creting cells.  (After  Haberlandt.) 

nous ' '  when  the  cells  are  torn.     In  the  lysigenous  form  the  secre- 
tion appears  in  the  individual  cells ;  subsequently  the  cell- walls  are 


FIG.  95.— Oil-gland  in  the  leaf  of  Hyper- 

icum  perforatum.     (After  Haberlandt.) 
h,  Protective  sheath  ;  s,  secreting  cells. 


FIG.  96.— "  Lysignian  "  oil-gland  in 
the  leaf  of  Dictamnus  albus. 
(After  Haberlandt.) 


dissolved  and  the  products  of  secretion  flow  together.     Example,: 
the  oil-bearing  epidermal  glands  of  Dictamnus  FraxineUa. 


PART  III. 

ORGANS  AND  SYSTEMS  OF 
ORGANS- 


"When  any  given  organ  develops  similar  or  dissimilar  lateral 
organs  we  speak  of  the  entire  structure  as  an  organ-system.  In 
such  a  system  there  are  members  of  different  order  and  members  of 
different  rank.  Members  are  of  a  different  order  when  they  have 
a  different  origin.  The  rank  of  different  members  is  dependent 
upon  a  physiological  inequality  ;  for  example,  aerial  members  with 
green  leaves  and  subterranean  storage-tissue  with  scaly  leaves  are 
physiologically  different. 

We  shall  now  treat  (1)  of  the  morphological  and  physiological 
differences  of  organs,  (2)  of  the  origin  and  arrangement  of  lateral 
organs  and  the  causes  of  such  arrangement,  (3)  of  the  difference  in 
the  development  of  the  members  of  a  system  of  similar  organs 
(branching),  which  will  finally  lead  us  to  the  discussion  of  inflores- 
cence. Although  I  have  taken  exception  to  NAGELI  and  SCHWEN- 
DENER  in  the  interpretation  of  fundamental  principles,  yet  the  gen- 
eral treatment  of  the  subject  matter  in  Part  III  is  adapted  from  the 
works  of  the  authors  mentioned.  As  to  the  descriptive  morphology, 
I  shall  adhere  to  RADLKOFER'S  method  'of  treatment,  and  more  espe- 
cially to  that  of  G.  "W.  BiscHOFF.1 

I.  THE  MORPHOLOGICAL  AND   PHYSIOLOGICAL 
RELATIONS  OF  ORGANS. 

A.  THE  PRINCIPAL  FORMS  OF  ORGANS. 

In  the  course  of  this  discussion  we  will  find  that  it  is  neces- 
sary to  add  physiological  properties  to  the  fundamental  morpholog- 

1  Hanclbuch  der  botanischen  Terminologie. 

155 


156  COMPENDIUM  OF  GENERAL  BOTANY. 

ical  differences  in  order  to  bring  out  the  characteristics  of  an 
organ. 

In  botany  an  organ  is  a  cell-portion,  a  cell,  or  a  cell-complex 
which  is  adapted  to  perform  a  definite  life  function  of  the  plant. 

Morphological  differences  of  organs  do  not  always  coincide  with 
physiological  differences.  Organs  that  are  equal  in  importance 
physiologically  may  differ  very  greatly  morphologically,  while 
organs  differing  physiologically  may  have  similar  morphological 
characters.  Compare,  for  example,  thorns  and  prickles,  tendrils 
and  climbing  sterns.  Morphological  definitions  are  dependent  upon 
the  history  of  development ;  physiological  definitions  upon  func- 
tion. Strictly  speaking,  morphology  treats  only  of  the  members  of 
a  plant-body,  while  physiology  treats  of  the  organs  (Sachs).  We 
usually  base  the  distinction  of  plant-organs  upon  morphological 
differences,  while  the  modification  or  formation  of  organs  is  based 
upon  physiology.  The  critical  features  of  such  a  procedure  will  be 
discussed  below. 

1.  The  thallome.     In  the  thallome  there  is  no  sharp  differentia- 
tion between  stem  and  normal  leaf  ;  this  organ  may  resemble  a  stem 
or  a  leaf,  or  it  may  resemble  both  organs  in  different  parts  of  the 
same    plant.       In    its   simplest  form    it   is   single-celled    and   not 
branched    (examples:    Diatom  acecK,   Desmidiacece),  or   it   may  be 
branched,  consisting  either  of  a  single  cell  or  of  a  few  cells.     The 
lateral  organs  of  the  alga  Scytonema  are  simply  repetitions  of  the 
mother-organ,  while  in  other  algse  (Caulerpa,  Fucacew,  Floridece) 
there  is  a  marked  distinction  between  the  main  plant-body  and  its 
lateral  organs;  the  latter  may  re  present  leafy  formations  or  root-like 
structures.     The  prothallium  of  ferns,  a  small  green   heart-shaped 
structure  found  on  the  soil  in  the  forest  or  in  flower-pots,  green- 
houses, etc.,  is  a  thallome.     A  thallome  is  therefore  an  independent 
vegetable  structure  devoid  of  organs,  with  perhaps  the  exception  of 
trichomes. 

The  following  organs  are  closely  related  to  each  other.  The 
thallome  may  occur  independently,  but  the  trichome,  caulome,  phyl- 
lorne,  and  root  cannot  occur  independently. 

2.  The   trichome  originates  from  the   superficial   (epidermal] 
cell-layer  of  various  organs,  or  more  rarely  from  the  epidermis  and 
cells  lying  beneath  the  epidermis ;  so  that  we  may  distinguish  be- 
tween epidermal  trichomes  and  tissue-trichomes  (emergences).     The 
spines  on  the  fruit  of  the  horse-chestnut,  for  example,  are  emer- 


ORGANS  AND  SYSTEMS  OF  ORGANS.  157 

gences.  The  trichomes  are  not  formed  with  any  regularity  or 
according  to  any  systematic  arrangement.  Epidermal  trichomea 
differ  greatly  in  form  (see  Epidermal  System,  p.  53). 

The  two  following  organs  • 

3.  Caulome  (stem-organ)  and 

4.  Phyllome    (leaf-organ)  are  so  intimately  related  that  they 
must  be  treated  together.     The  stem  (caulome)  is  really  the  central 
organ   which   bears  leaves  along  the  sides  below  the  apex.     The 
leaves  are  lateral  organs  on  the  apex  and  sides  of  the  stem  and  its 
branches  which  are  not  irregularly  formed   here  and  there,  but.  in 
general,  are  developed  acropetally,  that  is,  from  the  base  toward  the 
apex  (see  Fig.  101).     It  is  impossible  to  find  any  fundamental  dif- 
ferences between  the  internal  and  external  structure  of  stem  and 
leaf.     It  is  true  leaves   usually  present  an  expanded  surface,  but 
there    are   likewise   flat    stems   (Cactacece)   and   cylindrical   leaver 
(Conifer  CK]. 

5.  The  root  is  the  organ  whose  cell-forming  apex  is  covered  by 
a  protective  tissue,  the  root-cap,  and  which  never  bears  leaves.     In 
contrast  to  trichomes  and  phyllomes.  the  root  develops  en dogenously, 
so  that  it  must  force  its  way  through  some  tissue  before  it  can  come 
to  the  surface.      (The  term   "rhizome"  does  not  have  the  same 
meaning  as  root,  as  we  shall  learn  later.) 

B.  MODIFICATION  OF  ORGANS. 
(a)  Modifications  of  Stem  and  Root. 

Certain  modifications  of  the  caulome,  due  to  its  subterranean 
position,  are  of  special  physiological  importance.  Such  canlome- 
organs  are  without  foliage-leaves,  or  flowers.  These  modifications 
as  well  as  a  few  root-forms  will  now  be  briefly  discussed. 

The  following  are  the  subterranean  stem- modifications,  of  which 
there  may  be  intermediate  forms: 

(a)  The  rhizome  or  root-stock — stem-  and  leaf-organ  moderately 
developed. 

(b)  The  tuber — stem  enormously  developed,  leaves  very  small. 

(c)  The  l)ulb — stem  small,  leaves  very  large. 

At  this  point  we  shall  introduce  a  biological  classification  of 
plants;  that  is,  a  classification  derived  from  the  lire-processes  of 
plants. 


158  COMPENDIUM  OF  GENERAL  BOTANY. 

I.  Monocarpous  plants  (haplobioticce)  bear  fruit  only  once  and 
then  die.     This  occurs  in  one  year  in  annual  plants,  in  two  years  in 
biennial  plants ;  in   some  after  four  or  five  years,  as,  for  example, 
the  'Agave    americana.      (In    our    greenhouses   this   plant   bears 
flowers  only  after  about  forty  to  sixty  years.) 

II.  Polycarpous  plants  (anabioticce)  regularly  form  fruit  each 
year  on  one  and  the  same  plant- body.     Two  means  serve  to  main- 
tain  the  plant-species:  the   periodical   formation   of  seed,  and  the 
longevity  or  endurance  of  the  plant.     These  plants  may  again  be 
divided  into  two  groups  :  1,  the  aerial  stem  is  woody  and  endures 
as  such  for  a  long  time,  as,  for  example,  shrubs  and  trees,  some  of 
which  are  evergreen,  while  others  drop  their  leaves  ;  or  2,  the  stem 
is  herbaceous  and  dies  to  the  surface  of  the  soil  each  year,  but  begins 
to  grow  again  from  a  subterranean  perennial  stem.     These  are  the 
perennial  plants  in  the  narrower  sense,  and  in  them  occur  the  above- 
mentioned  subterranean  stem-modifications  which  serve  as  reservoirs 
for  reserve  food-materials  (starch,  water,  albumen,  etc.).     Typical 
rhizomes  occur  among  grasses  and  species  of  Carex  ;  bulbs  among 
Liliacece,  tubers  of  Solanum  tuberosum  (potato).     "  Runners  "  may 
serve   as   asexual    propagative   organs ;    that   is,  prostrate   lateral 
branches    which    have    developed    from    subterranean    buds  may 
develop  roots,  stems,  and  leaves  from  the  nodes. 

Some  of  the  aerial  stem-modifications  receive  special  names. 
The  culm  of  grasses  is  a  hollow  stem  with  nodes  at  the  attachment 
or  insertion  of  the  leaf  and  usually  branching  near  the  apex.  The 
flower-stalk  is  nearly  always  free  from  leaves  and  terminates  in  a 
single  flower  or  group  of  flowers.  The  culm  of  semi-grasses  (Cyper- 
acecB)  contains  pith  and  is  without  nodes.  There  are  tubers  with 
one  or  several  buds,  depending  upon  the  number  of  internodes 
represented.  The  potato  has  many  buds  situated  in  depressions 
and  surrounded  by  scaly  leaves.  A  peculiar  case  of  a  tuber  with 
one  bud  is  where  the  hypocotyledonous  member,  that  is,  the  portion 
of  the  stem  below  the  cotyledons,  becomes  thickened,  as  in  the 
horse-radish. 

The  conception  "  tuber  "  is  purely  morphological,  as  is  seen  from 
the  fact  that  orchid-tubers 1  are  thickened  secondary  roots.  In 
Spiraea  filipendula  secondary  roots  also  become  much  enlarged. 


1  The  more  precise  morphology  designates  these  as   "  tuberidia  "  instead  of 
''  tubers."     These  organs  furnish  the  officinal  mucilage  of  salep. 


ORGANS  AND  SYSTEMS  OF  ORGANS.  159 

The  main  root,  tap-root,  characterized  as  the  direct  elongation  of 
the  stem,  is  often  destroyed  and  its  functional  activity  is  taken  up 
by  the  lateral  roots.  In  plants  developed  from  tubers  and  bulbs 
(many  monocotyledonous  plants)  there  is  no  main  root. 

Ordinary  roots  take  up  water  and  soluble  substances  contained 
in  the  soil  (see  Physiology  of  Tissues,  II,  B),  and  serve  to  attach 
the  plant  firmly  to  the  soil.  In  warm  moist  climates  many  plants 
possess  aerial  roots  whose  physiological  importance  we  have  already 
learned  to  know.  In  certain  cases  (Pandanus,  for  example)  these 
aerial  roots  may  enter  the  soil  and  serve  as  organs  of  support ;  they 
may  even  form  the  only  support  for  the  stem.  In  other  tropical 
plants  the  branches  send  out  aerial  roots  which  elongate  and  form 
supporting  organs  (mangrove  trees  ;  JOHOW). 

(b)  Modifications  of  the  Phyllome. 

The  leaf-organ  also  presents  various  physiological  forms  or 
modifications.  The  observer  soon  learns  to  distinguish  germ-leaves 
(cotyledons),  cataphyllary  (scaly)  leaves,  foliage-leaves,  hypsophyllary 
leaves,  and  floral  leaves.  Before  discussing  these  in  particular  we 
shall  consider  briefly  the  general  morphology  of  the  phyllome. 

In  the  highest  type  the  leaf  may  be  divided  into  three  morpho- 
logical parts :  leaf-sheath,  petiole,  and  blade  (vagina,  petiolus  et 
lamina)  (Fig.  97). 

If,  however,  only  two  of  the  parts  mentioned  were  present,  it 
would  be  wrong  to  speak  of  it  as  an  undeveloped  or  imperfect  leaf; 
there  are,  for  example,  leaves  consisting  only  of  the 
sheath-portion,  as  the  bud-scales,  bulb-scales,  and  rhi- 
zome leaves;  these  are  nevertheless  highly  perfect. 
In  those  cases  where  one  or  the  other  of  the  parts 
mentioned  is  absent  it  is  because  it  would  be  useless; 
this  makes  the  part  that  is  present  so  much  more 
important  from  a  physiological  standpoint.  In  the 
discussion  of  the  mechanical  tissue-system  we  inci- 
dentally mentioned  the  mechanical  function  of  the 
leaf-sheath.  The  sheath  is  the  expanded  basal  por- 
tion at  the  base  of  the  petiole  or  at  the  base  of  the 
blade;  it  encloses  the  stem.  The  stipules  are  special  modifications 
of  the  leaf-sheath.  Example:  Asperula  odorata  ;  of  the  six  or 
eight  leaf-like  structures  arranged  in  a  whorl  two  are  true  leaves 


160  COMPENDIUM  OF  GENERAL  BOTANY. 

with  axillary  buds,  the  remaining  two  or  four  are  stipules. 1     (Func- 
tion of  grass-ligules  ?) 

The  petiole  is  the  stem-like  support  of  the  leaf-blade.  If  the 
petiole  is  absent,  the  leaf  is  said  to  be  "sessile."  Sometimes  a  leaf- 
portion  resembling  the  petiole  alone  is  developed,  usually  as  a  ten- 
dril. In  some  plants  the  petiole  is  flattened,  as  in  the  phyllodes  of 
Acacia ;  these  are  not  to  be  confounded  with  the  phyllocladea  of 
Ruscus,  for  example,  which  are  leaf-like  stems  and  bear  leaves 
themselves.  In  cross-section  the  petiole  usually  presents  the  appear- 
ance of  a  horseshoe;  such  structural  arrangement  serves  to  increase 
the  mechanical  support. 

The  Hade  terminates  the  petiole  of  the  sheath  as  the  true  leaf-ex- 
pansion. In  the  assimilating  foliage-leaves  it  is  strongly  developed, 
also  in  the  petals  of  the  corolla  ;  the  calyx  is  usually  a  modification 
of  the  sheath-portion.  It  is  not  intended  to  enter  into  an  extended 
discussion  of  the  morphology  of  the  blade,  though  some  such 
knowledge  is  necessary  in  order  to  understand  the  various  modifica- 
tions of  the  form  of  the  blade. 

Usually  the  blade  is  recognized  as  the  leaf-surface  or  simply  the 
leaf.  It  may  be  linear  (about  four  times  as  long  as  broad),  oval 
(about  twice  as  long  as  broad),  or  elliptical  (distinguished  from  the 
oval  by  the  angles  at  apex  and  base).  In  regard  to  the  base  the 
leaf  may  be  narrowed,  rounded,  cordate,  auriculate  or  eared  when 
the  inner  side  of  the  lobe  is  rounded,  hastate  or  halberd-shaped  when 
the  base  is  cut  straight  across,  sagittate  when  the  lobes  are  directed 
outward.  The  tip  or  apex  of  the  leaf  may  be  rounded,  blunt, 
obtuse,  mucronate,  acuminate,  truncate  when  it  seems  cut  across, 
emarginate  when  there  is  a  depression  at  the  apex,  obcordate  when 
the  depression  is  deep. 

If  the  leaf-margin  is  not  divided  or  cut,  it  is  said  to  be  entire; 
it  is  toothed  when  the  projections  at  the  margin  point  outward, 
serrate  when  the  projections  slant  forward,  crenate  when  the  pro- 
jections are  rounded  and  the  depressions  pointed,  sinuate  when 
projections  and  depressions  are  both  rounded.  Usually  the  leaf- 
surface  is  even,  sometimes  repand,  undulate,  or  wavy,  especially 
toward  the  margin  ;  or  it  may  be  variously  folded,  either  longi- 
tudinally, transversely,  or  radially. 


WARMING  (POTTER),  Handbook  of  Systematic  Botany,  1895. 


ORGANS  AND  SYSTEMS  OF  ORGANS.  161 

When  the  incisions  are  not  limited  to  the  margin,  but  extend 
more  deeply,  we  distinguish  : 

1.  Lobed   leaves   (fol.    lobatum),    when    the   incisions   do   not 
extend  quite  half-way  to  the  midrib  and  the  margins  of  the  lobes  are 
rounded. 

2.  Cleft  leaves  (fol.fissum),  when  the  incisions  do  not  extend 
quite  half-way  to  the  midrib  and  the  lobes  are  pointed. 

3.  Parted    leaves  (fol.  partitum\  when   the   incisions   extend 
more  than  half-way  to  the  midrib. 

4.  Divided   leaves  (fol.    sectum),  when  the  incisions  extend  to 
the  base  or  to  the  midrib. 

All  these  forms,  lobed,  cleft,  etc.,  are  again  separated  into 
palmately  and  pinnately  lobed,  cleft,  parted,  and  divided  accord- 
ing to  whether  the  direction  of  the  incisions  is  toward  the  base  of 
the  blade  or  toward  the  midrib. 

In  the  compound  leaf  the  blade  is  divided  into  entirely  separate 
parts ;  each  part  is  called  a  leaflet  (foliolum}.  It  really  seems  as 
though  the  petiole  were  branched,  each  leaflet  having  a  small  petiole 
of  its  own  by  which  it  is  attached  to  the  common  petiole.  We 
may  again  have  palmately  and  pinnately  compound  leaves.  Some- 
times the  difference  between  a  divided  simple  leaf  and  a  compound 
leaf  is  not  easily  recognized.  When  we  find  the  individual  leaflets 
jointed  or  articulated  to  the  common  petiole  in  a  way  similar  to 
that  in  which  the  latter  is  articulated  with  the  stem,  we  may  be 
certain  that  it  is  a  compound  leaf.  The  leaflets  may  be  entire, 
dentate,  serrate,  etc.  ;  or  lobed,  cleft,  parted,  etc. ;  thus  we  may 
have  twice  or  thrice  pinnately  or  palmately  compound  leaves.  In 
the  former  case  the  leaflets  are  called  pinnce,  in  the  latter pinnidce. 

Venation,  that  is,  the  arrangement  and  distribution  of  vascular 
bundles  in  the  leaf,  is  intimately  associated  with  the  form  of  the 
leaf-blade.  Most  monocotyledons  have  parallel-veined  leaves ; 
most  dicotyledons  have  netted-veined  leaves.  This  venation  may 
again  be  divided  into  pinnately  veined  and  palmately  veined. 

We  will  now  briefly  consider  the  modifications  of  the  leaf  men- 
tioned in  the  beginning  of  this  section  (b). 

1.  Cotyledons  (embryonic  leaves).  Of  these  the  monocotyledons 
have  one,  dicotyledons  two,  and  gymnosperom  few  or  many.  They 
constitute  the  first  leaf-like  structures  of  the  embryo,  appearing 
almost  without  exception  as  entire  lobes.  With  NAGELI  and  others 
we  may  designate  them  as  thallome  lobes,  since  true  leaves  make 


162  COMPENDIUM  OF  GENERAL  BOTANY. 

) 

their  appearance  later.  This  fact,  however,  has  no  bearing  on  the 
theory  of  descent  (evolution),  as  might  be  supposed.1  There  is 
no  doubt  that  our  most  highly  organized  plants  started  from  a 
single  cell;  of  this  ontogeny  has  given  abundant  proof.  But  to 
conclude  from  this  that  all  plants  in  their  successive  generations  are 
evolved  phylogenetically  is  strange  speculation.  From  arguments 
founded  upon  a  natural  basis  we  cannot  accept  such  a  hypothesis. 
r>  The  most  important  facts  in  regard  to  the  physiology  of  cotyle- 
dons have  already  been  mentioned  under  assimilation. 
X  2.  Cataphyllary  leaves.  These  leaves  occur  below  the  foliage- 
leaves ;  they  not  only  occur  near  the  base  of  the  stem,  but  may  be 
found  near  the  base  of  branches.  As  already  indicated,  they  are 
scaly  and  the  blade-portion  of  the  leaf  predominates.  The  bud- 
scales,  which  serve  to  protect  the  bud  during  the  winter  months, 
are  usually  such  cataphyllary  leaves.  As  the  name  indicates,  they 
are  situated  at  the  base  of  the  future  stem  or  branch ;  they,  of 
course,  are  situated  at  the  apex  of  the  stem  during  the  summer  and 
autumn,  that  is,  above  the  foliage-leaves  of  the  older  generation. 
The  foliar  structures  of  the  above-mentioned  subterranean  stem- 
organs  are  cataphyllary  leaves;  for  this  reason  the  rhizome,  the 
bulb,  and  the  tuber  are  sometimes  called  "  cataphyllary  leaf-stems." 

3.  Foliage-leaves.      The    green    leaves,    usually    recognized    as 
leaves,  are  the  typical  organs  of  assimilation.     Nearly  all  that  has 
been  stated  in  regard  to  the  special  morphology  and  physiology  of 
leaves  had  reference  to  the  typical  assimilating  leaves.     Movements 
to  place  them  in  suitable  positions  with  regard    to  sunlight,  etc., 
will  be  discussed  in  a  subsequent  chapter. 

4.  Hypsophyllary  leaves.    The  hypsophyllary  leaves,  also  called 


1  Nor  can  we  accept  HACKEL'S  "biogeiietic  law,"  which  states  that  phylogeuy 
is  repeated  in  ontogeny.  For  example,  the  embryo  of  the  ferns  (Ceratopteris) 
leaves  its  "thallome"  state  very  early  and  forms  the  beginnings  of  a  stem,  root, 
and  leaves,  although  "  phylogenetically  "  it  is  certainly  more  closely  related  to 
the  t.halloid  plants  than  to  the  phanerogamic  embryos.  If  its  thalloid  nature  is 
prominent  in  the  idioplasm,  why  does  it  leave  its  thallome  state  earlier  than  does 
the  embryo  of  phanerogams  ?  Moreover,  it  follows  (in  opposition  to  NAGELI) 
from  the  conceptions  of  stem,  leaf,  and  thallome  that  a  differentiation  into  stem 
and  leaf  must  be  preceded  by  a  thalloid  state,  since  leaf  and  stem  are  correlated 
terms.  Nothing  else  seems  possible  than  that  a  thalloid  structure  of  one  or  more 
cells  must  precede  the  formation  of  stem  and  leaf.  (Though  many  problems 
connected  with  the  theory  of  descent  are  still  unsolved,  yet,  in  general,  it  is  unde- 
niable that  the  pJiylogenetic  history  of  the  individual,  is  so  to  speak,  reflected  in 
the  ontogenetic  development. — TKANS.) 


ORGANS  AND  SYSTEMS  OF  ORGANS.  163 

bracts,  are  above  the  foliage-leaves  and  below  the  flowers.  They 
are  usually  of  a  more  simple  structure  than  the  true  leaves;  the 
petiole  is  wanting,  usually  the  sheath  and  blade  are  not  differ- 
entiated. They  function  as  organs  of  protection  for  the  young 
flower,  as  is  well  illustrated  in  the  bracts  of  the  genus  Allium  and  in 
orchids,  in  the  involucre  of  Compositor,  glumes  of  grasses,  etc.  The 
development  and  position  of  hypsophyllary  leaves  are  based  upon 
physiological  and  anatomical  (teleological)  requirements,  and  is  not 
merely  accidental.  They  occur  most  frequently  in  plants  without  a 
calyx,  since  they  supplant  the  function  of  that  organ. 

5.  Floral  leaves.  The  peduncle  terminates  in  the  receptacle 
which  bears  the  floral  leaves.  Their  function  is  to  aid  in  the  proc- 
esses of  reproduction  either  directly  or  indirectly.  By  the  term 
flower  is  understood  a  complex  organ,  a  bud  developed  into  sexual 
reproductive  organs  (EICHLER).  A  flower  is  n  modified  branch. 
In  the  inflorescence  we  therefore  have  to  do  with  a  branching  por, 
tion  of  a  stem. 

We  shall  consider  the  flower  with  its  various  so-called  leaf-modi- 
fications, as  calyx,  corolla,  stamens,  and  pistils,  in  Part  IV  (repro- 
duction) in  order  to  avoid  needless  repetition,  especiall"  as  function 
is  considered  to  be  of  prime  importance. 

In  conclusion  we  shall  add  a  few  remarks  on  the  coloring  in  the 
various  leaf-modifications.  The  green  color  of  foliage-leaves  is  of 
functional  importance  (assimilation) ;  likewise  the  variegated  color- 
ing of  floral  leaves  (fertilization  by  means  of  insects).  The  hypso- 
phyllary leaves  may  be  colored  to  perform  the  function  of  a  foliage- 
leaf  or  of  a  floral  leaf,  or  of  both  ;  likewise  the  calyx,  though  it  is 
usually  green.  The  cataphyllary  leaves  are  rarely  green;  sometimes 
they  are  variously  tinted,  though  the  colors  are  usually  not  brilliant ; 
often  they  are  white. 

CRITICAL  OBSERVATIONS  ON  THE  DISTINCTION  OF  ORGANS. 

As  already  stated,  the  term  "  organ  "  is  a  physiological  concep- 
tion. Yet  it  is  customary  to  classify  organs  upon  a  morphological 
basis,  especially  according  to  the  morphology  of  development.  In 
such  a  procedure  great  care  is  necessary  in  order  to  avoid  mistaken 
conclusions.  If  we  consider  the  thallome,  leaf,  stem,  root,  and 
trichome  as  the  five  chief  organs  of  plants,  it  will  not  be  found 
difficult  to  add  the  organs  of  reproduction  (since  they  originate  ia 


164  COMPENDIUM  OF  GENERAL  BOTANY. 

a  manner  similar  to  the  trichomes  or  leaves  (phyllome).  An  un- 
warranted procedure  is  to  conclude  that  the  reproductive  organs  are 
evolved  from  the  vegetative  organs,  or,  as  it  is  usually  expressed, 
"are  derived  phylogenetically."  The  advocates  of  the  theory  of 
descent  either  take  its  correctness  for  granted  or  seek  to  make  it  ap- 
plicable to  this  or  that  case.  We  shall  refrain  from  going  beyond 
the  conclusions  based  upon  observed  facts  into  the  realm  of  phan- 
tasy and  pure  speculation.  Also  the  classification  of  leaves  as 
"leaf-forms"  is  not  acceptable  to  those  who  wish  to  consider,  for 
example,  the  cataphyllary  leaves  as  phylogenetically  derived  from 
the  foliage-leaves.1  A  few  remarks  on  the  '*  transition  "  of  vegeta- 
tive leaves  into  reproductive  organs  shall  now  be  added. 

In  the  first  place  it  is  evident  that  the  stamens  and  foliage- 
leaves,  morphologically  considered,  are  both  leaves,  yet  the  differ- 
ence between  them  is  very  great  when  we  consider  each  as  to  its 
function  in  the  mature  state,  since  such  a  mode  of  treatment  is 
appropriate  here  as  well  as  it  was  in  regard  to  the  internal  organs 
(tissue-systems).  It  is  also  clear  that  we  cannot  conceive  of  the  ori- 
gin of  a  stamen  other  than  that  it  starts  as  a  small  wart-like  cellular 
protuberance  on  the  side  of  the  stem.  Finally,  it  is  also  clear  that 
the  young  stamen  will  take  such  a  course  in  its  development  as  will 
lead  to  the  formation  of  a  pollen-bearing  organ  rather  than  of 
a  foliage-leaf.  The  morphological  conception  of  an  organ  is  justifi- 
able, but  it  must  not  be  valued  too  highly. 

Between  the  involucre  and  starniniferous  flowers  of  the  Corn- 
positce  occur  the  so-called  neutral  flowers,  which  to  the  observer 
seem  to  be  formations  of  a  double  nature.  It  is,  however,  evident 
that  in  the  development  of  stamens  such  intermediate  states  are 
not  passed  through  ;  these  neutral  organs  can  hence  not  be  looked 
upon  as  states  of  transition.  Morphology  based  upon  facts  of  de- 
velopment points  out  the  great  similarity  between  stamen  and  leaf, 
between  most  carpels  with  their  ovules  and  divided  or  compound 
leaves;  this  similarity  is  further  emphasized  by  the  frequent  occur- 
rence of  the  apparent  reversion  of  the  floral  leaf  to  a  foliage-leaf. 
Every  observer  has  no  doubt  witnessed  such  phenomena.  But  to 
conclude  that  such  changes  are  evidence  of  the  evolution  of  repro- 
ductive organs  from  purely  vegetative  leaves  is  wholly  unwarranted  ; 
it  has  not  been  proven. 


1  WESTERMAIER,  Natur  und  Offenbanmg,  1893. 


ORGANS  AND  SYSTEMS  OF  ORGANS.  165 

It  would  be  useless  as  well  as  nearly  impossible  to  change  our 
present  terminology  ;  for  example,  the  expressions  stamen-leaf,  pis- 
til-leaf, etc.  It  is,  however,  necessary  to  call  attention  to  what  I 
believe  to  be  erroneous  tendencies. 

Palaeontology  cannot  produce  any  evidence  to  show  that  phan- 
erogams did  not  always  possess  vegetative  as  well  as  reproductive 
organs.  There  is  no  scientific  basis  for  the  assumption  that  our 
present  phanerogams  were  preceded  by  ancestral  forms  with  only 
vegetative  organs.1 

C.  THE  COMPLEX  ORGAN  :   SHOOT. 

The  relation  between  cauloine  and  phyllome  leads  to  the  follow- 
ing discussion.  The  leaf-bearing  caulome  is  called  a  shoot,  the 
young  shoot  is  called  a  bud.  The  stem- portion  between  two  suc- 
cessive leaves,  or,  in  case  more  that  one  leaf  occurs  in  the  same  hori- 
zontal plane,  between  two  successive  whorls  of  leaves,  is  called  the 
internode.  The  node  ("joint"  or  "knot")  is  that  portion  of  the 
•caulome  on  which  the  leaf  is  borne  or  inserted  ;  it  is  often  somewhat 
enlarged  and  differently  colored.  The  entire  habit  of  a  plant  de- 
pends in  a  high  degree  upon  the  length  and  thickness  of  the  inter- 
nodes.  In  the  youngest  stage  the  leaves  are  very  closely  crowded 


1  These  observations  by  the  author  may  be  of  value  in  creating  critical  thought, 
but  they  cannot  be  considered  as  arguments  against  the  theory  of  descent  (evolu- 
tion). To  those  transition-forms  occurring  among  the  Composites  might  be  added 
numerous  other  examples  ;  especially  interesting  is  the  case  of  NympJuxa  tuberosa, 
in  which  the  transition  from  green  leaf  through  petal  to  perfect  stamen  is  some- 
times almost  complete.  It  must,  however,  be  borne  in  mind  that  such  transitions 
nre  themselves  the  products  of  phylogenesis,  and  not  of  ontogenesis.  To  bring  about 
permanent  states  of  transition,  as,  for  example,  the  conversion  of  a  formative  cell- 
group  into  a  stamen  rather  than  a  leaf,  requires  at  least  millions  of  years,  as  the 
geologic  record  shows.  In  comparing  a  leaf  with  a  stamen  or  with  any  other 
organ  it  must  be  remembered  that  both  are  the  products  of  evolution,  and  that  the 
present  dissimilarities  did  not  exist  originally. 

To  my  knowledge  no  scientist  has  ever  denied  that  phanerogams  as  such  did 
not  always  possess  both  vegetative  and  reproductive  organs  ;  they  would  not  be 
phanerogams  if  they  did  not.  The  problem  is  to  trace  the  evolution  of  the  various 
organs,  and  to  show  how  they  are  connected  throughout  the  various  groups  of  the 
vegetable  kingdom. 

The  palaeoutologic  record  as  far  as  it  goes  bears  out  the  facts  of  evolution. 
Every  scientist  admits  that  the  geologic  record  is  of  necessity  broken,  but  even 
these  gaps  are  becoming  gradually  less  apparent. — TRANS. 


166  COMPENDIUM  OF  GENERAL  BOTANY. 

below  the  apex  of  the  stem  ;  the  internodes  are  therefore  very 
short,  later  many  of  them  become  much  elongated.  In  general, 
it  is  found  that  the  basal  nodes  remain  short,  followed  by  long 
nodes  in  the  leaf-bearing  region  and  again  by  short  nodes  near  the 
apex ;  the  phyllomes  are  correspondingly  crowded  near  the  base 
(basal  rosette  of  many  plants),  higher  up  they  are  farther  apart, 
then  again  more  crowded  near  the  apex.  In  the  caulome  of  u  un- 

o  ' 

limited "  growth  longer  and  shorter  internodes  frequently  alter- 
nate ;  in  such  cases  we  find  that  the  cataphyllary  leaves  are  crowded  ;. 
they  indicate  the  boundary  between  two  annual  growths.  Upon 
these  follow  foliage-leaves  on  elongated  nodes,  then  again  cata- 
phyllary leaves  on  shortened  nodes,  etc. 

Vertical  shoots  are,  as  a  rule,  structurally  alike  on  all  sides  ;  hori- 
zontal branches  and  twigs,  especially  such  as  rest  on  the  soil,  show 
considerable  difference  of  structure  between  the  upper  and  lower 
sides.  For  example,  it  is  found  that  the  leaves  on  the  horizontal 
stems  of  conifers  occur  along  the  sides  to  the  right  and  left;  in  some 
mosses  and  in  Selaginella  there  are  structurally  different  upper  and 
lower  leaves.  Upright  shoots,  therefore,  have  a  radial  structure, 
while  horizontal  organs  have  a  dorsiventral  structure  (SACHS). 
These  structural  differences,  which  are  dependent  upon  the  in- 
fluence of  gravity  and  sunlight,  also  modify  the  habit  of  plants.  The 
study  of  the  stem  and  branches  of  the  pine  will  make  clear  wThat 
has  just  been  stated. 

The  bud  is  either  terminal  or  lateral ';  in  the  latter  case  either 
axillary,  or  adventitious  when  its  position  is  at  indefinite  points 
along  the  stem  and  not  in  the  axil. 

Vernation  is  the  term  applied  to  the  position  of  leaves  in  the 
bud.  The  relative  position  of  several  leaves  in  the  bud  is  called 
wstivation.  Both  conditions,  compared  with  the  mature  state  of 
the  organs,  show  their  peculiarities. 

In  regard  to  vernation  the  simplest  case  is  where  the  leaf  lies 
flat  in  the  bud  ;  the  individual  leaf  may,  however,  be  bent,  folded, 
or  rolled,  either  longitudinally  or  transversely. 

Estivation  is  valvate  when  the  margins  of  the  leaf-organs  touch 
each  other,  or  imbricate  when  the  margins  overlap ;  this  latter  may 
again  be  spiral  or  quincuncial  (five-ranked),  etc. 

Before  passing  to  the  second  chapter  of  this  section  we  shall 
introduce  a  few  statements  in  regard  to  metamorphosis  and  correla- 
tion. 


ORGANS  AND  SYSTEMS  OF  OBGANS.  167 

D.    METAMORPHOSIS  AND  CORRELATION.     , 

It  is  highly  essential  that  every  one  who  devotes  his  attention 
to  the  different  tendencies  of  our  science  should  adhere  to  the 
purely  botanical  definition  of  metamorphosis.  It  would  of  course 
be  a  waste  of  time  and  energy  to  try  to  disprove  such  a  thing  as  the 
occurrence  of  metamorphosis  ;  however,  it  is  necessary  to  dispel  the 
erroneous  conception  that  in  metamorphosis  there  is  a  real  trans- 
formation of  one  organ  into  another.  Although  we  cannot  follow 
the  eminent  morphologist  GOBEL  in  his  explanation  of  organ  meta- 
morphosis l  (I  have  stated  my  objections  in  Natur  und  Offenbar- 
ung,  1893),  yet  I  agree  with  the  author  in  his  introductory  state- 
ments that  (1)  there  is  a  wide  difference  between  true  metamor- 
phosis and  the  metamorphosis  of  GOETHE  and  A.  BRADN,  and  (2)  in 
not  a  single  instance  have  we  been  able  to  prove  the  phylogenetic 
origin  of  any  leaf-formation  due  to  real  transformation.  An  impor- 
tant statement  from  so  eminent  an  authority. 

Cotyledons,  cataphyllary  leaves,  foliage-leaves,  and  floral  leaves 
show  such  great  similarity  in  their  early  stages  of  development  that 
one  might  well  speak  of  them  as  the  beginnings  of  members  of  the 
same  morphological  value.  They  are  simply  more  or  less  extended 
cellular  protuberances  or  warts  upon  lateral  portions  of  the  stem. 
However,  in  their  subsequent  development  they  are  transformed 
into  organs  having  widely  different  functions.  Even  what  was 
originally  the  beginning  of  a  leaf  may  not  always  develop  into  a 
leaf:  it  may  develop  into  a  prickle,  tendril,  or  suctorial  foot — organs 
which  are  no  longer  called  leaves.  Such  a  change  in  development 
is  known  in  the  vegetable  kingdom  as  metamorphosis. 

Based  upon  the  above  statements  we  may  accept  the  follow- 
ing definition  as  given  by  SACHS  in  the  year  1868  : 2  Metamorphosis 
is  the  varied  development  of  members  of  the  same  morphological 
value  for  the  purpose  of  adapting  them  to  definite  functions. 

One  might  incline  to  the  view  that  since  metamorphosis  is 
identical  with  the  normal  development  of  the  organs  it  is  unneces- 
sary to  speak  of  them  as  "  transformations."  It  must,  however,  be 
observed  that  the  term  metamorphosis  implies  that  the  originally 


1  Beitrage  zur  Morphologie  und  Physiologic  des  Blaltes,  Botanische  Zeitung, 
1880. 

2  Lehrbuch  der  Botanik  ;  Vines'  translation  of  the  edition  of  1874. 


168  COMPENDIUM  OF  GENERAL  BOTANY. 

equal  morphological  value  is  subsequently  followed  by  a  physio- 
logical dissimilarity.  Occurrences  in  the  vegetable  kingdoms  teach 
us  that,  for  example,  not  all  tendrils  and  thorny  structures  originate 
in  like  manner,  that  is,  from  rudiments  known  as  foliar  protuber- 
ances (tendrils  of  Lathyrus  and  spines  of  Berberis] ;  some  originate 
in  the  manner  of  branches  (the  tendrils  of  the  grape,  the  thorns  of 
Rhamnus  cathartica).  The  conceptions  "  thorn  "  and  "  tendril " 
are  therefore  physiological,  and  not  morphological.  The  second 
feature  of  metamorphosis  is  that  morphologically  unequal  organs 
may  be  equal  in  value  physiologically.  Of  this  occurrence  physio- 
logical anatomy  knows  so  many  examples  that  the  entire  phenome- 
non has  come  to  be  looked  upon  as  a  law  of  nature.  The  foregoing 
has  shown  us  what  metamorphosis  in  the  botanical  sense  means. 
It  is  hoped  that  it  has  also  made  clear  that  it  does  not  mean  the 
transformation  of  one  organ  into  another? 

There  is  still  another  interesting  condition  to  be  mentioned  : 
the  correlation  of  the  growth  of  organs.  This  is  readily  understood 
from  the  standpoint  of  teleology.  One  example  will  suffice  to 
illustrate  what  is  meant.  If  one  cuts  away  the  young  shoots  of  a 
potato-plant,  new  lateral  shoots  will  be  formed  which  would  other- 
wise have  developed  into  tubers ;  that  is,  organs  which  were 
originally  intended  to  remain  underground  and  form  storage-tissue 
for  reserve  material  under  certain  conditions  will  form  aerial  organs 
developing  green  leaves  having  the  function  of  assimilation.  This 
phenomenon  can  readily  be  explained  from  the  standpoint  of 
physiology,  but  cannot  be  rationally  explained  from  the  causal- 
mechanics  of  organ-development,  as  SACHS  is  inclined  to  believe 
(see  ref.,  p.  167). 

II.   OBIGIN    AND    POSITION    OF  LATEKAL  ORGANS, 

AND  THE  CAUSES  FOE  THEIR  DEFINITIVE 

POSITION. 

How  is  a  system  of  organs  formed?  or,  more  specifically,  how 
and  when  do  new  organs  develop  from  those  already  existing? 
Upon  what  is  the  final  position  of  the  organ  dependent  ? 

These  are  the  questions  which  shall  interest  us  now.  As  is  in- 
dicated, there  is  a  difference  in  the  origin  of  organs  as  well  as  in 


1  GOBEL'S  metamorphosis  of  organs  I  have  discussed  elsewhere;  also  the  sub- 
ject of  "correlation  "  as  opposed  to  the  views  of  SACHS  (see  citation  above). 


ORGANS  AND  SYSTEMS  OF  ORGANS. 


169 


their  succession.  The  position  and  arrangement  of  young  organs 
are  also  different  from  their  later  position  and  arrangement  (final  or 
definitive  position). 

There  are  not  less  than  seven  different  places  of  origin  for  the 
various  organs  of  the  more  highly  organized  plants.  They  are  as 
follows  : 

1.  The  epidermis.     In  it  the  tric/wmes,  also  the  "  emergences," 
with  the  aid  of  more  deeply  seated  layers,  have  their  origin. 

2.  The  apical  portion  of  the  stem  gives  rise  to  branches. 

3.  The  terminal  portion  of  roots  gives  rise  to  secondary  roots 
(dichotomy). 

4.  The  meristem  (formative  tissue)  of  the  stem-organ  immedi- 
ately below  the  apex  gives  rise  to  leaves. 

5.  The  tissue  in  the  axils  of  leaves  gives  rise  to  axillary  shoots.1 

6.  The  cambium  and  all  other  meristematic  tissues  within  the 
epidermal  layer  of  various  organs,  such  as  stem,  leaf,  and  root,  give 
rise  to  adventitious  branches  and  roots. 

7.  The  pericambimn  of  the  root  gives  rise  to  the  normal  root- 
branches. 

Adventitious  formations  (6)  and  normal  root-branches  (7)  origi- 
nate endogenously,  as  opposed  to  the  exogenous  origin  of  organs 
mentioned  under  1-5  inclusive. 

From  the  various  groups  of  cellular  plants  we  shall  select  the 
following  cases  for  discussion  : 

(a)  Among   many  algae   branching  of  the   thallome   proceeds 
from  the  apical  cell  ;  well  exemplified  in  FlorideoB  (Fig.  98,  dia- 
gramatic). 

(b)  In    some    algae   (Cladophora, 
CharacecB)  the  branches  proceed  from 
certain  body-cells  (Fig.  99).     It  may 
be  that  any  or  all  body-cells  can  de- 
velop   branches,  or   it   may  be   that 
only  certain   special  cells  have   that 
power. 

(c)  In   mosses  the   conditions  are 
quite  different.     At  the  apex  of  the 
stem  of  the  moss  there  is,  as  a  rule,  a 


FIG.  98. 


two-edged  "  or  a  three-sided 

1  Among  angiosperms  there  is,  as  a  rule,  a  young  shoot  for  each  leaf-axil  ;  in 
gymnosperms  this  is  not  the  rule  (this  may  readily  be  observed  in  Taxus  and 
other  conifers). 


170 


COMPENDIUM  OF  GENERAL  BOTANY. 


pyramidal  cell.  In  the  latter  case  each  segment  may  develop  a 
leaf  (see  Fig.  100,  diagramatic  apical  views).  If  each  successive 
segment  develops  more  strongly  on  one  side,  there  will  be  produced 


FIG.  99. 


FIG.  100  B. 


a  spiral  arrangement  of  the  leaves  (see  Fig.  100  B,  diagramatic 
apical  view).  In  still  other  cases  the  halves  of  each  segment  (either 
side  by  side  or  above  each  other)  may  develop  leaves  or  branches. 
(LEITGEB  has  studied  the  development  of  the  mosses  more  par- 
ticularly.) 

In  regard  to  the  position,  inclusive  of  the  succession  of  develop- 
ment, of  lateral  organs  we  may  distinguish  the  following  cases : 

I.  Organs  are  irregular  as  to  origin  and  position.     Example : 
trichomes  upon  other  organs. 

II.  The  origin  and   position  of  organs  may  be  in  longitudinal 
rows,  as  is  the  case  in  secondary  roots  formed  from  the  pericam- 
bium.     The  number  of  rows  is  dependent  upon  the  number  of 
primordial  xylem-groups.     The  succession  of  their  development  is, 
as  a  rule,  acropetally,  therefore  the  youngest  branch  is  always  nearest 
the  apex  of  the  root.     Longitudinal  rows  of  lateral  organs,  such  as 
secondary  roots  and  leaves,  also  occur  in  creeping  ("  dorsiventral") 
organs. 

III.  Frequently  organs  originate  and  are  arranged  in  whorls,  as 
is  seen  in   the  case  of  leaves  and   branches.     Two  or  more  lateral 


ORGANS  AND  SYSTEMS  OF  ORGANS.  171 

organs  may  develop  from  the  same  horizontal  plane  of  the  mother- 
organ.  Example :  the  two-leaved  whorl  of  the  Labiatce,  the  three- 
leaved  whorls  of  Juniper  us. 

IV.  The  organs  are  arranged  in  spiral  lines.  The  so-called 
"spiral"  position  of  leaves  and  branches  will  be  more  fully  dis- 
cussed in  the  following  chapter. 

A.  SPIRAL  ARRANGEMENT  OF  LEAVES.     THEORIES  OF  PHYLLOTAXY. 

A  line  continuing  around  the  stem  in  the  same  direction  and 
cutting  the  various  lateral  organs  by  the  shortest  path  is  called  the 
ground-spiral. 

This  ground-spiral,  according  to  more  recent  investigators,  is  not 
necessarily  a  genetic  line  (genetic  spiral) ;  that  is,  the  leaves  need  not 
follow  this  line  in  the  order  of  their  development,  although  they 
may  follow  a  spiral  line  subsequently.  We  shall  base  our  state- 
ments upon  the  studies  of  ScnwENDENER.1 

As  indicated  above,  there  are  only  a  very  few  cases  in  which  the 
genetic  line  corresponds  to  the  ground-spiral,  as  in  the  leaf-form- 
ing segments  of  the  apical  cell  of  mosses  (Fig.  100).  In  other 
plant-groups  the  spiral  arrangement  is  different,  even  among  those 
in  which  an  apical  cell  cuts  off  segments  in  succession  along  a 
spiral  line.  It  has  been  observed  (Schwendener)  that  in  the  fern 
the  course  of  the  leaf-spiral  is  independent  of  the  segmentation- 
spiral  of  the  apical  cell.  Also  in  Equisetum  scirpoides  there  seems 
to  be  no  fixed  relation  between  the  \e&i-whorl  and  the  spirally  pro- 
duced segments  of  the  apical  cell.  The  flowers  on  the  disk  of 
IleliantTius  are  evidently  not  always  developed  acropetally  corre- 
sponding to  the  ground-spiral.  The  fact  that  apical  cell-growth  in 
the  stem  of  dicotyledons  is  not  well  known  in  all  cases  adds  to  the 
difficulty  of  finding  the  relation  of  the  leaf-spiral  to  the  spiral  of  the 
apical  cell-segments.  Therefore  it  cannot  be  maintained  that  the 
spiral  arrangement  of  the  leaves  in  the  ferns,  dicotyledons  and 
monocotyledons,  corresponds  to  a  definite  spiral  position  of  foliar 
protuberances  near  the  apex  of  the  stem.  With  Schwendener  we 
must  consider  the  following  of  importance  in  giving  a  clearer 
knowledge  of  the  subject.  The  young  lateral  organs  or  leaf -begin- 
nings, which  appear  as  small  protuberances,  touch  each  other;  they 


1  Mechanische  Theorie  der  Blattstellung,  1878.     HOFMEISTER  is  recognized  as 
having  done  the  preliminary  work  in  this  line. 


172  COMPENDIUM  OF  GENERAL  BOTANY. 

.are  bodies,  and  not  mathematical  points.  Each  young  organ  touches 
at  least  two  of  the  preceding  organs — so  to  speak  rests  upon  them, 
similar  to  balls  piled  upon  each  other.  We  will  not  discuss  the 
causes  for  the  formation  of  an  organ  ;  they  are  unknown.  It  is 
evident  that  there  must  be  a  supply  of  food-substances  in  order  that 
an  organ  may  develop;  why  this  supply  takes 
place  neither  physiology  nor  morphology  can 
explain  (causal-mechanical  explanation).  We 
may,  however,  recognize  the  factors  which 
determine  the  position  of  the  developing 
lateral  organs ;  these  factors  are  (1)  the  rel- 
ative  size  of  the  organs  already  existing  and 
e  new  organ>  aT1d  (2) tne  direct  contact 
of  the  previously  formed  and  the  new  organ. 

The  fact  that  the  initial  °^ans  at  the  base  of 

stem  showing   the  ar-    the  stem   are  usually  of  constant  size  while 
rangement  of  the  leaves.     the  kter  initial  ^^  ^^^  sina]ler  in  an 

acropetal  direction  is  of  morphological  importance  (Fig.  101). 

Gradual  decrease  in  the  size  of  organs  toward  the  apex,  or  press- 
ure due  to  the  growth  in  length  and  thickness  of  the  stem,  and  the 
growth  of  organs  themselves  produce  phenomena  which  may  be 
expressed  as  follows  :  Existing  contact-lines  disappear  and  new  con- 
tact lines  appear. 

Let  us  now  continue  the  theoretical  discussion  of  this  subject. 

The  horizontal  distance  between  two  successive  leaves,  or  in 
other  words  the  angle  which  the  median  planes  of  the  two  leaves 
enclose,  is  known  as  their  divergence.  Usually  when  the  leaf- 
divergence  is  given  as  ^-,  f,  f,  etc.,  it  is  found  that  the  degrees  corre- 
sponding to  these  fractions  (120°,  144°,  135°,  etc.)  are  only  approxi- 
mately correct. 

In  the  divergence  expressed  by  £  two  leaves  are  separated  by 

o£*rjo 

=  120°.     A  necessary  result  is  (1)  that  the  fourth  leaf  should 

3 

be  vertically  above  the  first,  since  three  divergences  make  the  360° 
of  the  circumference,  and  that  (2)  there  are  three  vertical  leaf-rows. 
In  f  there  are  five  divergences  and  two  turns  around  the  stem 
before  we  find  two  leaves  in  a  vertical  line.  It  follows  that  there 
must  be  five  vertical  rows,  since  the  leaves  0  and  5,  1  and  6,  2  and 
7,  3  and  8,  etc.,  are  vertical.  In  other  words,  the  fraction  indicat- 
ing the  angular  divergence  of  leaves  may  be  explained  as  follows: 


ORGANS  AND  SYSTEMS  OF  VKGANS. 


172 


The  numerator  indicates  the  number  of  turns  about  the  stem,  begin- 
ning with  one  leaf  and  terminating  at  the  first  leaf  vertically  above  ; 
the  denominator  indicates  the  number  of  vertical  rows. 

There  are  two  methods  for  representing  the  leaf-divergence 
graphically:  first,  projection  upon  a  horizontal  plane,  as  in  Fig.  102, 
which  represents  the  divergence 
J- .  This  method  shows  the  verti- 
cal rows  very  clearly.  The  other 
method  is  that  of  representing 
it  upon  the  plane  of  a  cylinder 
rolled  out  flat.  This  brings  out 
the  spiral  lines  very  beautifully, 
as  shown  in  Fig.  103,  which  illus- 
trates the  divergence  f. 

The  number  of  vertical  rows 
also  gives  the  number  of  leaves 
between  two  successive  members 
of  a  series,  as  will  be  seen  from  a 
close  inspection  of  the  figures ; 
for  example,  in  Fig.  103  eight  vertical  rows  are  shown,  hence  the 
name  eight-ranked. 

Likewise  the  parallel  diagonal  lines  cutting  the  leaf-organs  also- 
indicate  the  number  of  intervening  leaves.     For  example,  in  the 


PIG.  102. 

(After  Sachs.) 


FIG.  103. 

direction  ab  (Fig.  103)  this  number  is  five,  in  the  direction  cd  it 
is  three.  These  relations  can  be  very  easily  studied  in  the  cones  of 
conifers.  It  must  be  borne  in  mind  that  this  numerical  relation 


174  COMPENDIUM   OF  GENERAL  BOTANY. 

has  no  essential  bearing  upon  the  ground-spiral;  they  are  simply 
"  spiral  lines"  or  "  secondary  spiral  lines."  Such  secondary  spirals 
become  very  distinct  when  the  organs  are  closely  crowded,  as  they 
are  in  pine-cones. 

B.  THE  DETERMINATION  OF  A  DIVERGENCE. 

It  is  almost  impossible  to  count  the  vertical  rows  as  well  as  the 
turns  about  the  stem  when  the  angles  of  divergence  are  very  small. 
In  such  a  case  it  is  customary  to  start  from  a  given  leaf  (marked  in 
some  way)  and  to  determine  (1)  the  number  of  distinct  diagonal 
rows,  (2)  the  number  of  distinct  rows  crossing  the  former  in  an 
opposite  direction,  usually  at  nearly  right  angles.  It  is  thus  possible 
to  number  the  organs  upon  a  slip  of  paper,  always  starting  from  the 
marked  leaf  or  starting-point.  By  drawing  a  line  through  two 
leaves  having  the  same  number  the  horizontal  plane  is  found  ; 
then  let  fall  a  perpendicular  cutting  the  horizontal  and  the  leaf  at 
the  starting-point.  The  angular  divergence  may  now  be  directly 
measured,  or  by  the  aid  of  the  vertical  line  the  number  of  turns 
about  the  stem  may  be  counted,  which  will  determine  the  fraction 
of  divergence. 

The  fractions  £,  £,  f,  f,  T53,  &  (180°,  120°,  144°,  135°,  etc.) 
give  the  (approximate)  divergences  of  most  frequent  occurrence ; 
the  entire  series  is  therefore  called  the  "  normal  series."  Further 
particulars  will  be  given  below. 

By  way  of  demonstrating  what  has  been  said,  we  will  consider 
a  few  examples  from  nature.  The  cones  of  the  red  or  the  white 
pine  show  the  divergence  ¥8T  with  great  regularity  ;  the  series  five 
and  eight  predominate  in  the  secondary  spirals.  The  given  relation 
between  the  size  of  the  stem  and  the  size  of  the  secondary  organs 
is  therefore  quite  constant,  since  the  divergence  in  the  stem  and  in 
the  cone  is  the  same. 

It  is  also  easy  to  determine  the  position  of  the  first  leaves  on  the 
axillary  shoots  of  dicotyledons  (shrubs).  The  pressure  of  the  axillary 
leaf  and  the  position  of  the  primary  axis  tend  to  make  the  first  two 
leaves  develop  to  the  right  and  left.  The  cause  for  the  sinistrorse 
or  dextrorse  course  of  leaf-spirals  is  also  mechanical ;  this  is,  however, 
not  demonstrable  without  microscopic  examinations  (A.  WEISSE,  of 
Schwendener's  school). 


ORGANS  AND  SYSTEMS  OF  GROANS.  175 

O.  THE  MECHANICAL  THEORY  OF  PHYLLOTAXY  AND  THE  IDEALISTIC 
CONCEPTION  OF  NATURE. 

Because  of  the  important  bearing  of  this  subject  upon  the  true 
idealistic  and  the  so-called  mechanical  conception  of  nature  I  can- 
not refrain  from  commenting  upon  SCHWENDENER'S  theory  of  phyl- 
lotaxy. By  idealistic  I  do  not  mean  anything  fantastic  and 
dreamy,  but  rather  that  clear  and  definite  conception  of  the  laws  of 
nature  as  given  by  the  Creator,  and  of  matter  as  created  by  him  ; 
furthermore,  that  causality  does  not  cease  where  causal-mechanics 
fail ;  that,  moreover,  the  usual  tendency  of  natural  history  or  science 
to  indicate  this  or  that  as  something  "given  "  points  to  the  imma- 
terial Giver  as  the  highest  Being  and  the  CREATOR  of  all.  It  would 
be  wrong  to  suppose  that  SCHWENDENER'S  mechanical  theory  of 
phyllotaxy  had,  so  to  speak,  destroyed  the  very  foundation  of  the 
idealistic  conception  of  phyllotaxy.  Schwendener's  mechanical 
principle  of  causality  is  far  from  satisfactory.  The  thoughtful  in- 
vestigator would  naturally  expect  that  the  mechanical  theory  would 
trace  complicated  phenomena  to  simpler  causes  wrhich  must  then  be 
considered  as  granted  or  given. 

The  question  why  certain  divergences  occur  most  frequently  was 
considered  of  great  importance  by  the  opponents  of  Schwendener's 
new  theory.  This  question  was  proposed  by  C.  DE  CANDOLLE  in 
the  year  1881.  The  divergence  fractions  ^,  J,  -|,  f,  y5¥,  etc.,  ex- 
pressed in  degrees  approach  the  limiting  value  137°  28'  30", 
which  is  the  ratio  of  the  golden  section  (sectio  aurea)  to  the  circum- 
ference of  a  circle.  This  is  only  true  of  the  normal  series;  other 
series  have  different  limiting  values.  The  principal  reason  why  the 
earlier  advocates  of  the  idealistic  theory  (C.  SCHIMPER  and  A.  BRAUN) 
failed  to  substantiate  their  doctrine  was  because  these  authors  treated 
the  organs  under  consideration  as  mathematical  points,  and  not  as 
bodies  in  actual  contact.  To  them  the  fractions  of  divergence  con- 
stituted the  part  " given,"  while  to  us  they  are  simply  the  necessary 
mechanical  results  of  certain  given  relations.  Although  we  reject 
the  spiral  theory  of  Schimper  and  Braun,  we  must  not  allow  "  num- 
ber mysteries"  to  carry  us  too  far,  as  they  evidently  did  Schwen- 
dener,  at  least  in  his  leading  work  (1878).  In  1883  *  this  author 
undertook  the  consideration  of  the  question  proposed  by  de  Candolle. 


Sitzungsbericbte  der  Berl.  Akademie. 


176  COMPENDIUM  OF  GENERAL  BOTANY. 

His  explanation  of  the  phenomenon  shall  soon  claim  our  attention. 
We,  from  our  point  of  view,  deduce  from  it  that  the  finding  of 
mechanical-causal  relations  does  not  imply  that  all  idealistic  con- 
ceptions of  nature  are  thereby  destroyed,  but  rather  that  it  assists  in 
exposing  and  making  clear  the  great  simple  ideas.  Schwendener 
has  rightly  named  his  theory  of  phyllotaxy  the  accessory  theory 
(i;  Anschlusstheorie").  It  is  always  necessary  to  assume  a  basis, 
or,  so  to  speak,  a  frame,  upon  which  or  within  which  the  arrange- 
ment of  contiguous  and  variously  superimposed  organs,  such  as  leaves 
and  branches,  must  take  place.  This  assumed  basis  for  monocotyle- 
dons is  the  two-ranked  arrangement  of  the  single  cotyledon  and  the 
succeeding  leaves.  See  the  copy  of  Scbwendener's  figure  (Fig.  104). 

In  dicotyledons  this  "given  "  basis  is  the  crossed  position  of  the 
opposite  leaf-pairs,  an  arrangement  initiated  by  the  two  cotyledons. 
While  the  normal  spiral  of  monocotyledons  may  be  produced  by 
other  means  than  the  acropetal  decrease  in  size  of  the  foliar  begin- 
nings, that  is,  by  slow  displacement  due  to  longitudinal  pressure,  it 
is  evident  that  such  pressure,  producing  displacement  of  equally 
large  organs  in  dicotyledons,  would  only  convert  the  opposite  whorl 
into  a  twisted  whorl.  But  if  one  member  of  the  leaf-pair  is  smaller, 
or  if  other  irregularities  appear  in  the  crossing  of  the  pairs,  the 
above  normal  series  1,  2,  3,  5,  8,  etc.,  will  of  necessity  be  devel- 
oped provided  there  is  a  gradual  decrease  in  the  size  of  the  organs 
in  an  acropetal  direction. 

According  to  Schwendener's  explanation,  it  is  again  the  given 
basis  of  the  system,  as  well  as  the  deviations  from  absolute  regu- 
larity which  necessarily  work  together  to  produce  the  spiral  ar- 
rangement of  organs  in  the  dicotyledons. 

Schwendener  also  studied  coniferous  seedlings  which  begin  with 
a  whorl  of  3-8  cotyledons,  and  established  the  remarkable  fact  that, 
in  spite  of  the  unequal  initial  position  of  organs  and  irregular  addi- 
tions of  subsequent  organs,  the  final  result  is  nearly  always  a  normal 
spiral.  These  small  deviations  mentioned  above,  which  are  of 
normal  occurrence,  are  the  essential  mechanical  factors  in  the  ar- 
rangement of  lateral  organs.  TEITZ,  a  pupil  of  Sch wendener,  carried 
on  a  series  of  experiments  which  seemed  to  prove  that  longitudinal 
tensions  proceeding  from  the  vascular  system  of  leaves  and  ex- 
tending along  the  connected  bundles  of  the  stem  determine  the 
position  of  lateral  organs.  The  causes  leading  to  the  position  of 
leaves  mav  therefore  be  stated  as  follows :  The  given  'basis  of  the 


ORGANS  AND  SYSTEMS  OF  ORGANS. 


177 


system,  the   variations   in  size   of  the  contiguous  organs,  and  the 
tension-effects  of  the  leaf-trace  bundles. 

The  mechanical  results  of  the  morphological  factors  are  the  pre- 
dominance  of  the   normal   series  of  divergences  (limiting  value: 


FIG.  104. — Diagramatic  representation  of  the  transition  from  the  alternating 
two-ranked  arrangement  to  the  spiral  arrangement  caused  by  the  diminution 
in  the  size  of  the  organs.  (After  Schwendener.) 

relation  of  the  golden  section,  extreme  and  mean  proportion.  (See 
above.)  This  phenomenon  is,  therefore,  not  purely  morphological 
(Schimper,  A.  Braun,  Bravais)  but  mechanically-morphological ; 
for  it  represents  mechanical  results  associated  with  almost  constantly 


178  COMPENDIUM  OF  GENERAL  BOTANY. 

recurring  morphological  relations.  With  this  statement  I  draw 
only  one  deduction  from  the  investigations  of  Schwendener  and  his 
pupils.  This  is  done  in  order  to  meet  the  superficial  conclusions  of 
some  scientists,  that  the  newer  scientific  teaching  in  regard  to 
phyllotaxy  does  not  leave  a  trace  of  the  idealistic  (in  the  author's 
sense)  in  the  plant  creation. 

True  and  rational  idealism  is  not  at  all  disturbed  by  such  mate- 
rialism. The  academic  speech  of  DU  BOIS-REYMOND  (Berlin,  July  8, 
1880)  had  only  an  oratorical  value  when  he  stated  that  Schwen- 
dener could  pride  himself  as  being  one  of  those  investigators  who 
had  aided  in  driving  the  "misty  forms  of  vitalism  "  out  of  their 
"  last  hiding-place."  The  great  fame  of  Schwendener  is  due  to  his 
achievements  in  the  domain  of  pure  scientific  teleology.  His  au- 
thority as  a  botanist  has  been  recognized  for  years,  and  will  no 
doubt  stand  for  many  years  to  come. 

In  this  problem  of  phyllotaxy  repeated  attempts  have  been 
made  to  give  a  teleological  explanation,1  but  the  real  progress,  which 
we  owe  to  Schwendener,  has  been  made  with  reference  to  another 
branch  of  our  science. 

The  advance  made  evidently  lies  in  that  we  can  say :  that  me- 
chanical relations — contact-  and  pressure-effects — are  the  immediate 
causes  for  the  appearance  of  the  divergences.  However,  there  are 
many  problems  still  unsolved.  "Why  do  certain  plant-groups  (mono- 
cotyledons, dicotyledons,  gymnosperms)  produce  as  a  "  basis  "  one 
cotyledon  with  alternating  leaves,  or  two  equally  large,  or  three  to 
eight  nearly  .equally  large  cotyledons?  Further,  why  does  the 
gradual  reduction  in  the  size  of  the  organs  not  appear  regularly  in 
plants  where  the  divergence  is  approximately  f  ?  Why  are  vascular 
bundles  (leaf-trace  bundles)  so  united  laterally  that  they  must 
produce  certain  tensions  at  suitable  periods  ?  These  and  similar 
questions  are  still  unanswered.  We  must  admit  that  the  chief 
merit  of  Schwendener's  (in  part  also  of  Hofmeister's)  discoveries  lies 
in  the  fact  that  he  has  refuted  the  spiral  theory,  and  in  the  intro- 
duction of  mechanical  factors  into  the  domain  of  morphology. 
SCHIMPER,  BRAUN,  as  well  as  the  BEAVAIS  and  NAUMANN  brothers 
looked  upon  lateral  growth,  especially  the  leaf-formations,  as  always 
following  certain  lines.  There  can  be  no  genetic  significance  at- 
tached to  the  ground-spiral,  nor  to  the  secondary  spirals  or  "  par- 


Depending  upon  adaptation  to  light  and  space. 


ORGANS  AND  SYSTEMS  OF  ORGANS. 


179 


astichies,"  nor  to  the  vertical  rows  or  "  orthostichies  "  (Naumann). 
We  can  only  say  that  the  position  of  organs  is  dependent  upon  the 
size,  form,  and  the  relative  position  of  new  organs  and  organs 
already  formed.  The  activity  of  the  leaf-forming  apex  of  the  stem 
is  under  the  mechanical  influence  of  organs  already  formed.  The 
fact  that  many  leaf-beginnings  with  wide  divergences  really  corre- 
spond to  the  arrangement  of  the  organs  on  the  ground-spiral  is  not 
contradictory  to  what  has  been  stated. 


III.  DIFFERENCE  IN  THE  POWER  OF  DEVELOP- 
MENT OF  THE  MEMBERS  OF  EQUAL  MORPHO- 
LOGICAL VALUE.  CLASSIFICATION  OF  ORGAN- 
SYSTEMS. 

(After  NAGELI  and  SCHWENDENER.) 

A  system,  as  represented  in  Fig.  105,  A,  may  be  formed  in  dif- 
ferent ways,  and  its  difference  as  compared  to  other  systems  de- 
pends upon  the  mode  of  development.  We  will  distinguish  two 
forms  of  development,  the  monopodial  and  the  sympodial.  A 
monopodium  is  formed  according  to  the  plan  shown  in  Fig.  105,  By 
a  sympodium  according  to  the  plan  shown  in  Fig.  105,  C. 


In  the  monopodium  (B)  the  primary  axis  represents  the  median 
line  and  grows  most  strongly,  the  lateral  branches  cease  to  grow 
early,  and  do  not  branch.  In  the  sympodium  (C)  the  upper  part 


180 


COMPENDIUM  OF  GENERAL  BOTANY. 


of  the  primary  axis  turns  from  the  median  line  and  develops  a  sec- 
ondary branch  or  axis ;  the  secondary  axis  takes  the  direction  of 
growth  of  the  primary  axis,  and  finally  divides  again,  forming  an 
axis  of  the  third  order;  this  third  axis  bears  the  same  relation  to 

the  second  axis  as  the  second  axis  bears 
to  the  first,  and  so  on.  This  forms  what 
is  known  as  a  "  sympodium  "  or  pseudo- 
axis.  The  rhizome  of  Polygonatum 
multiflorum  is  a  good  example  (Fig.  106). 
The  expression  sympodium  implies  that 
the  organ  is  composed  of  different podiar 
that  is  of  shoots  or  branches  of  different 
orders. 

Two  organ -systems  may  be  exactly 
alike  in  the  beginning  but  may  by  wholly 
different  in  the  mature  state.  This  statement  is  contradictory  to 
what  was  said  at  the  beginning  of  this  chapter.  It  can  readily  be 
supposed,  and  it  is  actually  true  that  a  spike  and  an  umbel  are  alike 
at  the  beginning  of  their  formation.  The  attempt  to  co-ordinate 
development  and  the  mature  state  is  liable  to  cause  confusion.  One 
must  either  trace  the  mature  state  back  along  the  line  of  its  devel- 
opment or  vice  versa,  in  order  to  have  a  correct  understanding  of 
the  true  conditions. 

To  trace  the  development  of  an  organ-system  is  not  always  an 
easy  task.  An  example,  which  incidentally  introduces  us  to  a  very 
difficult  chapter  of  morphology,  will  show  that  under  certain  con- 


FIG.  106.— Rhizome  of 

gonatum  multiflorum. 
a,  Bud  ;  6,  basal  portion  of  stem  ; 


c  and  d,  stem-scars, 
and  Landois.) 


(After  Krass 


FlG.  107.     (Diagramatic.) 


r 

FlG.  108.      (Diagramatic.) 


ditions  it  is  impossible  to  judge  of  the  course  of  development  from 
a  study  of  the  mature  state.  Very  frequently  there  are  deviations 
from  the  normal  axillary  branching.  This  I  will  attempt  to  explain 


ORGANS  AND  SYSTEMS  OF  ORGANS. 


181 


with  the  aid  of  EICHLER'S  theoretical  figures  (107  and  108),  used  to 
illustrate  the  condition  of  things  as  they  occur  in  Datura  Stra- 
monium. A  normal  development  of  bracts  and  axillary  products 
would  produce  a  structure  similar  to  that  shown  in  Fig.  108.  The 
actual  appearance,  however,  we  find  to  be  as  shown  in  Fig.  107. 
Only  in  the  youngest  shoots  (III)  are  the  conditions  normal,  at 
least  for  the  leaves  a"  and  ft".  Leaf  ft',  Fig.  107,  although  a  bract 
of  III,  has  been  raised  from  its  normal  position,  shown  in  Fig.  108. 
Every  bract  of  the  entire  inflorescence  thus  shifts  position  as  further 
shown  by  a  and  ft ;  normally  they  should  have  the  same  position 
relatively  to  &,  as  a"  and  ft"  have  to  ft' .  The  axes  I,  II,  etc.,  ter- 
minate in  flowers. 

A.  INFLORESCENCE. 

Branching  in  the  hypsophyllary  region,  the  terminal  branches 
bearing  few  or  several  flowers,  occurs  more  frequently  than  a  single 
floral  axis  with  a  single  terminal  flower.  Such  branching  (with  or 


\ 

\ 

\ 


FIG.  109. 


without  hypsophyllary  leaves),  therefore,  represents  more  than  one 
flower,  and  is  known  as  the  inflorescence.     We  distinguish  the  fol- 


182  COMPENDIUM  OF  GENERAL  BOTANY. 

lowing  types  of  inflorescence,  of  which  there  may  occur  interme- 
diate forms,  usually  classed  with  one  or  the  other  type. 


(a)  Itacemose  Inflorescence. 

Primary  and  secondary  axes  exist.  Primary  axis  does  not 
terminate  in  a  flower,  secondary  axes  not  branched,  usually  many, 
terminating  in  flowers. 

1.  JRaceme.     Primary  axis  long,  secondary  axes  short. 

2.  Spike.     Primary  axis  long.     Secondary  axes  wanting  or  very 
short. 

Subforms :  spadix,  primary  axis  fleshy  ;  catkin,  primary  axis 
often  pendulous  and  falling  off  after  blossoming ;  cone,  seminifer- 
ous scales  woody. 

3.  Umbel.     Primary  axis  short  or  compressed,  secondary  axes 
comparatively  long. 

4.  Head.     Primary   axis   short   and   cone-shaped   or  flattened, 
secondary  axes  wanting. 

The  following  are  the  plants  representing  the  types  mentioned  : 
1,  CruciferoB ;    2,  Plantago   (for  the   subforms:   Aroidece, 
Pinus) ;  3,  Umbelliferce  •  4,  Compositor. 


(b)  Paniculose  Inflorescence. 

Axes  all  terminate  in  flowers  and  branch  repeatedly;  secondary 
axes  of  the  first  order  predominate,  decreasing  in  length  and  in  the 
frequency  of  branching  with  the  increase  of  the  orders. 

Panicle,  as  exemplified  in  Alisma  Plantago. 

Umbels  with  terminal  flowers  are  at  the  same  time  paniculose 
and  racemose. 

(c)  Cicinnose  Inflorescence. 

Repeated  branching,  each  axis  bearing  only  one  lateral  branch, 
which  extends  above  the  mother-branch. 

To  this  inflorescence  belong  the  scorpioid  and  helicoid  cymes  as 
well  as  the  dichasium.  In  the  two  former  the  secondary  axes  are 
more  or  less  at  right  angles  to  the  primary  axis,  in  the  latter  more 
or  less  parallel  to  the  primary  axis. 


ORGANS  AND  SYSTEMS  OF  GROANS.  183 

1.  Scorpioid  cyme  (cicinnus,  cyme,  half  cyme) ;  secondary  axes 
are  arranged  alternately  to  the  right  and  left.     Example  :  Drosera. 

According  to  GOBEL'S  investigations,  the  inflorescence  of  the 
JSorraginece  cannot  be  included  here.  It  is  rather  a  dorsi-ventral 
raceme. 

2.  Helicoid  cyme  (bostrychoid  cyme,  bostryx) ;  secondary  axes 
all  on  the  same  side  of  the  primary  axis.     Example  :  Hypericum 
perforatum. 

3.  Dichasium.     This  is  really  a  slight  deviation  from  the  panic- 
ulose  type  in  that  the  primary  axis  divides  into  two  equally  strong 
branches  (Silene). 

Different  types  of  inflorescence  may  occur  on  the  same  plant, 
or  the  same  type  may  be  duplicated  on  the  same  stalk.  In  this  way 
complex  inflorescences  are  formed.  Umbelliferce  have  double  um- 
bels. Among  GraminecB  small  spikelets  unite  to  form  a  panicle 
(oats),  or  again  unite  to  form  a  spike.  . 

B.  RANK  AND  SUCCESSION  OF  SHOOTS. 

Above  the  statement  was  made  that  there  was  a  difference  in 
the  "  rank  "  of  various  organs  in  a  system  as  well  as  a  difference  in 
"  order."  While  the  orders  are  determined  by  the  origin  and  de- 
velopment of  members,  the  difference  in  rank  of  various  members 
of  a  system  depends  upon  physiological  inequality.  As  a  rule,  each 
member  develops  secondary  or  lateral  members  of  the  same  or  next 
higher  rank.  The  arrangement  of  branches  in  the  inflorescence 
absolutely  necessary  to  the  development  of  flowers  is  usually  differ- 
ent from  those  branchings  not  necessary,  usually  known  as  "  acces- 
sory branches  "  (Bereicherungsprosse). 

Case  1.  The  primary  axis,  or  axis  of  the  first  order,  bears  an 
apical  flower  :  "  uniaxial"  flowers,  one  rank.  Example  :  Helleborus 
niger. 

Case  2.  A  member  of  the  second  order  is  necessary  to  develop 
a  flower:  "biaxial"  plants,  two  ranks.  Example:  Paris  quadri- 
folia  allows  the  axis  of  the  first  order  to  grow  beneath  the  soil  as  a 
rhizome  bearing  cataphyllary  leaves.  In  the  axil  of  the  third  cata- 
phyllary  leaf  there  is  formed  a  vertical  member  of  the  second  order 
which  terminates  in  a  flower  (A.  BRAUN). 

Case  3.  Flowers  are  formed  on  members  of  the  third  order: 
" triaxial "  flowers,  three  ranks.  Example:  Lathyrus.  The  mem- 


184  COMPENDIUM  OF  GENERAL  BOTANY. 

bers  of  the  first  order  develop  leafy  shoots ;  the  members  of  the 
second  order  develop  floral  spindles  (axes  of  inflorescence) ;  the 
members  of  the  third  order  finally  develop  flowers. 

The  condition  of  affairs  in  the  genus  Pinus  is  especially  note- 
worthy. Long  shoots  alternate  with  short  shoots.  The  leaves  (in 
clusters  of  two  or  more)  occur  on  the  short  shoots  ;  the  long  shoots 
bear  scaly  leaves  from  the  axils  of  which  the  short  shoots  are 
developed. 


PART   IV. 
REPRODUCTION. 


INTRODUCTION. 

In  the  process  of  reproduction  germs,  or  in  other  words  foun- 
dations for  new  individuals,  are  formed.  These  germs  usually 
separate  from  the  mother-plant  when  mature ;  sometimes  they  re- 
main united  to  the  mother-plant  for  a  shorter  or  longer  time,  or 
even  during  the  entire  life-period.  First  case :  The  germs  soon 
become  separated ;  in  this  case  they  have  special  structural  adapta- 
tions for  the  purposes  of  protection,  distribution,  etc.,  and,  above 
all,  special  physiological  properties.  The  most  important  repro- 
ductive germs  belonging  here  have  specific  names :  seeds  (phan- 
erogams), spores  (cryptogams).  Second  case :  The  germs  remain 
in  organic  union  with  the  mother-plant  during  the  entire  life- 
period  or  only  for  a  short  time,  (a)  In  mosses  this  union  exists 
during  the  entire  life-period  of  the  plant,  (b)  In  ferns  the  daugh- 
ter-plant is  set  free  by  the  gradual  decay  and  disappearance  of  the 
mother-plant  (prothallium).  (e?)  In  propagation  by  means  of  bulbs, 
conns,  runners,  stolons,  etc.,  the  daughter- plant  is  made  indepen- 
dent by  the  gradual  disappearance  of  that  part  which  unites  it  to  the 
mother-plant.  Daughter-  and  mother- plant  may  then  exist  side  by 
side  independent  of  each  other. 

Reproduction,  or  the  formation  of  new  plant-individuals,  is 
rarely  limited  to  one  method.  In  the  same  plant  there  are  usually 
two  or  more  methods  of  reproduction.  The  difference  consists 
either  (1)  in  that  the  germs  are  formed  by  different  parts  (organs) 
of  the  mother-plant ;  or  (2)  that  one  germ  is  formed  sexually,  the 
other  by  one  or  several  of  the  various  asexual  methods ;  or  (3)  that 

185 


186  COMPENDIUM  OF  GENERAL  BOTANY. 

the  germs  themselves  and  the  plants  proceeding  therefrom  are 
different. 

We  can  now  recognize  two  categories  of  phenomena  which  may 
both  be  observed  on  the  same  plant  at  different  periods.  When 
different  methods  of  reproduction  are  united  in  the  same  plant- 
individual,  we  are  not  concerned  with  alternation  of  generation. 
If  different  methods  of  reproduction  do  not  occur  in  the  same  indi- 
vidual, but  alternate  with  the  successive  generations  of  a  plant,  we 
speak,  in  general,  of  alternation  of  generation.  By  alternation  of 
generation  we  therefore  mean  the  unequal  behavior  of  the  succes- 
sive generations  of  the  same  plant  with  regard  to  the  mode  of 
reproduction.  Concerning  the  first-mentioned  phenomenon  we 
will  not  have  much  to  say;  considerable,  however,  in  regard  to 
alternation  of  generation. 

Let  A  and  B  represent  different  methods  of  reproduction  (for 
example,  sexual  and  asexual)  ;  they  may  be  so  distributed  through 
the  generations  1,  2,  3,  4,  5,  6,  etc.,  that  1,  3,  5,  etc.,  are  the  result 
of  the  method  A  ;  2,  4,  6,  etc.,  of  the  method  B.  Of  very  fre- 
quent occurrence  is  that  form  of  alternation  of  generation  in  which 
method  B  is  common  to  a  series  of  successive  generations,  while 
method  A  occurs  in  only  one  generation  ;  then  another  series  of 
method  B,  etc.  The  following  scheme  will  illustrate  this  : 

Series  of  Generations. 


MM 

BBBB 

\ 
B 

A 

B 

\          \ 

Jj           xJ 

B 

1 
B 

A 

B 

B... 

Methods  of  Reproduction. 

In  the  case  of  alternation  of  generation  the  different  forms  of 
reproduction  are  equal  in  value  in  so  far  as  they  are  necessary  to 
the  maintenance  of  the  plant-species.  The  same  may  be  said  of  all 
forms  of  reproduction.  When  there  is  no  alternation  of  genera- 
tion, but  simply  a  combination  of  different  methods  of  reproduction 
in  the  same  individual,  then  these  various  methods  are  of  unequal 
value,  because,  as  a  rule,  one  form  of  reproduction  shows  itself  to 
be  constant  and  more  essential,  and  usually  occurs  at  the  conclusion 
of  development,  while  the  others  (non-essential)  make  their  appear- 
ance earlier.  Example  :  a  plant  which  finally  produces  seeds  sex- 
ually, that  is,  from  flowers,  may  in  the  course  of  its  life-history  be 


REPRODUCTION.  187 

propagated  from  stolons,  runners,  corms,  etc.  Should  these  latter 
means  of  propagation  fail  to  appear,  the  plant  could,  nevertheless, 
continue  its  existence. 

At  first  glance  the  above  general  considerations  and  statements 
in  regard  to  reproduction  may  not  seem  to  have  been  very  fortu- 
nately chosen.  However,  the  student  on  entering  more  deeply 
into  the  phenomena  coming  under  this  category  will  soon  recognize 
that  the  foregoing  introductory  statements,  in  which  the  author  has 
followed  KAGELI'S  concept  of  the  subject,  are  sufficient  to  place  the 
essentials  of  the  endless  variety  of  phenomena  under  a  few  com- 
prehensive heads. 

Germ-formation  is  very  frequently  sexual,  as  has  already  been 
stated.  The  male  and  female  organs,  which  are  essential  in  this 
form  of  reproduction,  permit  of  the  recognition  of  three  different 
forms,  dependent  upon  the  relative  position  of  these  organs. 

1.  Hermaphroditism :  male  and  female  organs  are  in  imme- 
diate proximity,  for  example,  in  phanerogams  in  the  same  flower ; 
or  on  the  same  axis  (among  vascular  cryptogams  on  the  same  pro- 
thallium). 

2.  MonoBcie :  male  and  female  organs  are  on  the  same  plant,, 
but  on  separate  axes ;  that  is,  the  flowers  are  unisexual. 

3.  Diweie :  male  and  female  organs  are  distributed  upon  dif- 
ferent individuals  of  the  same  species. 

A  large  number  of  flowers  are  hermaphroditic  (perfect,  bi- 
sexual), for  example,  our  cereals,  fruit-trees,  legumes,  the  poppy, 
etc. ;  the  birch,  oak,  hazelnut,  and  most  conifers  are  monoecious ; 
willows  are  dioecious.  Monoacie  and  dioecie  occurring  together 
form  didiny. 

Before  entering  upon  the  special  discussion  of  the  phenomena 
of  reproduction  it  is  important  to  introduce  an  observation  on 
systematic  botany.  The  essentials  of  our  plant-system  are  taken 
from  the  domain  of  reproduction,  and  wre  may  add  that,  as  far  as 
mosses,  vascular  cryptogams,  gymnosperms,  and  angiosperms  are 
concerned,  it  is  more  than  probable  that  no  other  factors  will  sup- 
plant in  importance  those  of  reproduction.  Algae  and  fungi  are 
separated  from  each  other  by  the  presence  or  absence  of  chloro- 
phyll, and  both  are  separated  from  the  leafy  mosses  by  the  absence 
of  leaf  and  stem ;  but  within  the  algal  and  fungal  groups  them- 


188  COMPENDIUM  OF  GENERAL  BOTANY. 

selves  the  factors  of  reproduction  are  utilized  in  establishing 
classes,  orders,  and  genera.  From  this  we  may  draw  the  conclu- 
sion that  in  a  book  like  the  one  before  us,  in  which  taxonomy  is 
not  more  fully  treated,  the  special  chapters  on  reproduction  must 
also  give  a  general  concept  of  the  systematic  arrangement  of 
plants. 

I.  EEPRODUCTION  AMONG  CKYPOTGAMS. 

We  will  speak  first  of  the  reproduction  of  cryptogams  in  gen- 
•eral  as  compared  with  that  of  phanerogams.  Generally  the  seeds 
of  cryptogams  are  called  spores  ;  they  usually  consist  of  one  or  of 
&  few  cells  and  are  mostly  microscopic  in  size.  In  contradistinc- 
tion thereto  the  seeds  of  phanerogams  are  larger  and  of  a  more 
complicated  structure ;  they  consist  of  several  parts.  The  perfect 
phanerogamic  embryo  within  the  seed-coverings  has  essentially  the 
structure  of  a  bud. 

Very  frequently  the  spores  of  cryptogams  are  formed  by  asexual 
methods,  and  not  as  the  result  of  fertilization.  (SACHS  '  proposed 
the  term  conidia  ["gonidia"]  for  all  thallophyte-spores  produced 
asexually;  EICHLER,'  using  the  same  term,  applied  it  to  the  asexual 
motionless  spores  of  fungi ;  while  WARMING  wishes  the  term  applied 
only  to  the  asexual  thallophyte-spores  produced  exogenously.  It 
would  no  doubt  be  appropriate  to  follow  the  proposition  of  SACHS.  3) 
The  seeds  of  phanerogams  are,  however  the  direct  product  of 
fertilization. 

There  is  also  a  series  of  cryptogamic  spores  which  are  the  imme- 
diate product  of  two  cells  reacting  upon  each  other.  These  spores 
are  called  oospores  (egg-spores)  when  the  two  cells  reacting  upon 
each  other  are  externally  very  different ;  zygospores  (zygotes)  when 
the  uniting  cells  seem  to  be  entirely  or  almost  entirely  alike :  the 
latter  process  is  called  conjugation. 

Most  spores  pass  through  a  period  of  rest  (resting- stage). 
With  the  maturation  of  the  spores  the  plant  for  a  time  ceases 


1  Compare  GOBEL'S  Grundzuge  der  Systematik. 

2  Syllabus,  1886. 


3  The  term  spores  is,  in  general,  also  applicable  to  the  reproductive  organs  of 
the  so-called  "  higher  "  cryptogams — mosses  and  vascular  cryptogams  ;  they  are 
also  produced  asexually. 


REPROD  UCTION.  1 89 

to  exist  as  far  as  that  particular  generation  is  concerned,  as.  for 
example,  during  the  winter,  or  during  periods  of  dryness. 
These  spores  ("  resting-spores ")  usually  develop  at  the  next 
period  of  vegetation  (spring,  rainy  season).  On  the  other  hand 
some  spores  develop  soon  after  their  maturation.  They  are 
usually  endowed  with  a  delicate  membrane,  as  distinguished  from 
the  resting-spores,  which  have  a  more  firm,  usually  colored,  mem- 
brane. Such  are  the  u  swarm-spores, "  so  called  because  they 
can  move  about  in  the  water  until  they  prepare  themselves  for 
germination.  As  soon  as  they  are  ready  to  develop  they  come  to 
rest  or  fasten  themselves  in  some  suitable  place.  (Algae  and  some 
fungi.)  Sexual  reproduction  is  not  known  to  occur  in  all  crypto- 
gams ;  many  investigators  now  agree  with  BREFELD  that  it  does 
not  occur  among  fungi.1  Among  the  remaining  cryptogamic 
groups — algse  (at  least  the  great  majority),  mosses,  and  vascular 
cryptogams — sexual  reproduction  undoubtedly  occurs.  The  anther- 
ids  are  the  male  sexual  organs  (among  cryptogams);  they  contain 
the  fertilizing  elements,  the  spermatozoids.  The  oogonidia,  (egg- 
receptacle),  or,  when  more  complicated  in  structure,  the  archegoniay 
are  the  female  sexual  organs ;  they  contain  the  egg-cell. 

The  spermatozoids  are  either  very  minute  oval  cells  or,  among 
the  more  highly  differentiated  cryptogams,  spiral  threads.  These 
threads  are  usually  supplied  with  two  cilia  (organs  of  motion)  at 
the  thinner  anterior  end ;  the  other  end,  which  is  usually  thicker, 
contains  plasm.  The  basal  substance  of  spermatozoids  (hence 
exclusive  of  cilia),  according  to  more  recent  investigations  (SCHMITZ, 
STRASBURGER,  ZACHARIAS),  consists  of  ' (  nuclein, ' '  that  is,  nuclear 
substance. 

The  oogonium  contains  the  egg-cell.  In  its  simplest  form  the 
oogonium  consists  only  of  a  covering  for  the  egg-cell.  The  egg- 
cell  is  frequently  enclosed  in  a  special  organ  known  as  the  arche- 
gonium ;  in  its  form  it  usually  resembles  an  Indian  club  of  variable 
length.  In  the  archegonia  of  mosses  and  vascular  cryptogams  one 
may  recognize  a  shorter  or  longer  "  neck  "  and  an  enlarged  base 
(venter)  containing  the  egg-cell.  The  figures  will  assist  in  illus- 
trating and  explaining  what  has  just  been  stated.  They  refer  to 
algse,  mosses,  and  vascular  cryptogams.  Fig.  110  illustrates  the 

1  Perhaps  also  true  of  lichens  ;  as  already  stated,  STAHL's  observations  have  not 
been  verified.— TRANS. 


190 


COMPENDIUM  OF  GENERAL  BOTANY. 


FIG.    111.  —  Sexual    organs    of 
Vaucheria  sessilis. 

Off,  Oogonium  ;  a,  antheridium. 
(After  Sachs.) 


FIG.  110. — Various  stages  in  the  conjugation 
of  Spirogyra  longata. 
(X  550.)    (After  Sachs.) 


Fig.  112.—  A,  Rupturing  anther- 
idium of  Funariahygrometrica 
(moss);  B,  magnified  spermato- 
zoid  in  the  mother-cell  ;  c,  free 
spermatozoid  of  Potytrichum. 
(After  Sachs.) 


REPRODUCTION. 


191 


processes  of  conjugation  in  Spirogyra  longata ;  the  upper  portion 
of  the  figure  shows  two  segments,  the  cell-walls  of  which  begin  to 
form  projections  at  a ;  at  b  projections  are  in  contact.  Further 
progress  is  shown  at  A  ;  at  B  the  final  stages  are  shown.  Such 
conjugating  cells  are  called  " gametes."  "  Zoogametes  "  is  the 


B 


FIG.  114. — Various  stages  of  the  antberidial  devel- 
opment of  Adiantum  capillus  (I,  II,  III), 
p,  Prothalliutn  ;  a,  antheridium  ;  s,  spermatozoid  with  at- 
tached remnant  of  the  mother-cell  (6).    (After  Sachs.) 


FIG.  113.  —  Funnria  liygro- 
tnetrica. 

A,  Archegonia  (a)  on  the  apex  of 
the  stem  between  the  leaves  (6)  ; 
B,  magnified   archegonium  (in 
glycerin)  ;    6,    ventral     portion 
with   oosphere  ;  h,  neck   of  ar- 
chegonium  ;  w,  mouih  of  arche-  FIG.    115. — Longitudinal  section  of  the    archego- 
faf'ter"1'  fertilization ) °P^( Af te?      nium  of  Adiantum  capMu*,  before  fertilization. 
Sachs.)  h,  Neck  ;  s,  ventral  canal-cell  ;  e,  oosphere,    (After  Sachs.) 

term  applied  to  conjugating  swarm-spores.  Fertilization  among 
Vaucheria  differs  very  distinctly  from  that  among  Spirogyra ;  in 
the  former  the  oogonium  og  (Fig.  Ill)  is  quite  different  from  the 
antheridium  #;  osp  in  E  is  the  oospore  containing  fat-  or  oil- 
globules. 


192 


COMPENDIUM  OF  GENERAL  BOTANY. 


A.   FORMS  OF  REPRODUCTION  AMONG 


Although  the  phenomena  under  discussion  differ  very  greatly  r 
we  are  enabled  to  see  (among  algae)  a  well-marked  relationship  ; 
there  is,  in  general,  an  alternation  of  generation  between  sexual 
and  asexual  methods. 

Among   Desmidiaoece  (unicellular   algse)   asexual  reproduction 

by  division  alternates  with  reproduction  by  the  conjugation  of  mo- 

tionless gametes  (see  Fig.  19  in  regard  to  reproduction  by  division). 

Peculiar  and  interesting  conditions  are  met  with  among  the 

Diatomacew,1  a  group    of   unicellular    yellowish-green    algse    en- 

closed by  a  silicious  mem- 
brane characterized  by 
very  beautiful  and  deli- 
cate striations  and  mark- 
ings. A  highly  delicate 
organization  associated 
with  great  reduction  in 
size  characterizes  these 
truly  marvellous  creat- 

ures.      (E  H  R  E  N  B  E  R  (>, 

1835.  OTTO  MULLER, 
Berlin,  is  at  present  well  known  as  a  specialist  on  diatoms.)  Space 
will  not  permit  a  fuller  discussion  of  the  delicate  structural  markings  ; 
we  can  only  mention  them  in  so  far  as  they  are  concerned  with  the 
processesof  reproduction.  The  two  parts  of  the  silicious  shell  of  the 
diatom  fit  each  other  as  do  the  body  and  cover  of  a  pasteboard  box. 
For  a  series  of  generations  reproduction  is  the  result  of  simple  divi- 
sion, hence  asexual  ;  then  follows  a  special  sexual  generation  (conju- 
gation), which  is  again  followed  by  division,  and  so  on  (see  Figs.  116 
and  LIT). 

The  following  statements  are  based  upon  direct  observation. 
(1)  Every  division  of  a  cell  forming  a  diatom-individual  (after 
cell-wall  formation  and  separation  of  the  two  cells)  gives  rise  to  one 
(A)  daughter-cell,  equal  in  size  to  the  mother-cell,  and  one  (B) 
smaller  daughter-cell.  (2)  There  is  no  growth  in  length  ;  as  a  result 
the  smaller  individuals  must  continually  increase  in  number.  The 


A 

FIG.  116. — Diagramatic 
tation  of  two  diatoms, 
view. 


B 


resenv 
teral 


FIG.  117.— Top 
view  of  dia- 
tom. 

(Berthold       and 
,  Landois  ) 


1  PFITZER  made  very  important  investigations  of  this  group. 


REPRODUCTION.  193 

species  would  therefore  be  gradually  reduced  to  such  small  size  as 
to  render  existence  impossible.  Extinction  due  to  decrease  in  size 
is  avoided  by  two  methods.  The  first,  after  certain  pauses,  fully 
restores  the  original  size  of  the  individual.  This  is  accomplished 
as  follows :  From  time  to  time  two  small  individuals  unite  with 
the  escape  and  fusion  of  the  cell- contents.  This  conjugation 
gives  rise  to  cm  exceptionally  large  individual,  sometimes  two. 
The  second  method  is,  so  to  speak,  corrective,  in  that  it  tends  to  re- 
tard the  decrease  in  size.  OTTO  MULLEB  '  has  discovered  the  fol- 
lowing law  of  development :  The  smaller  of  the  two  daughter -cells 
requires  twice  as  long  a  period  for  the  next  division  as  the  larger 
cell.  The  large  spores  formed  by  conjugation  are  called  auxospores, 
and  are  sometimes  formed  from  a  single  individual  (without  conju- 
gation). 

Protococcoideas,. — Either  vegetative  reproduction  by  division, 
or  sexual  reproduction  by  the  union  of  swarming  gametes  which 
differ  in  external  appearance. 

Confervoidece. — Asexual  reproduction  by  means  of  swarm- 
spores  ;  sexual  reproduction  by  conjugation  ( Ulothrix).  Anther- 
ids  and  oogonia  are  formed  in  some  cases  (Oedogonium,  Bid- 
bochaetce).  From  PRINGSHEIM'S  classical  investigations  of  the  alga 
Oedogonium  I  select  the  following  :  The  oospore  formed  during  the 
previous  vegetative  season  produces  four  swarm-spores  which  de- 
velop into  new  filamentous  algae.  Swarm-spores  are  also  formed 
from  the  vegetative  algal  threads.  The  oospore  is  the  result  of  the 
fertilization  of  the  egg- cell  by  means  of  the  sperrnatozoids  which 
enter  through  an  opening  in  the  covering  of  the  oogonium.  The 
sperrnatozoids  are  produced  in  two  ways :  either  directly  from  the 
cells  of  an  ordinary  filament,  or  from  a  small  few-celled  male  plant 
(Zwergmannchen).  The  latter  is  developed  from  an  "  andro- 
spore,"  a  peculiar  swarm-spore  which,  after  liberation  and  swarm- 
ing, comes  to  rest  and,  attaching  itself  in  some  suitable  spot,  devel- 
ops a  few  small  cells.  From  these  cells  the  spermatozoids,  which 
finally  escape  and  fertilize  the  egg-cell,  are  formed. 

Among  Characece  and  Vaucheriacece  there  occurs  a  sexual 
propagation,  besides  sexual  reproduction  which  is  highly  specialized 
in  the  former  group.  Among  Characece  propagation  is  accom- 


From  the  study  of  Melosira  arenaria,  Ber.  cl.  Deutsch.  Bot.  Ges.5  I,  1883 


194  COMPENDIUM  OF  GENERAL  BOTANY. 

plished  by  means  of  the  vegetative  protonema  (Zweigvorkeime) ; 
in  the  latter  group  occasionally  by  means  of  swarm-spores  (A. 
BRAUN,  PRINGSHEIM). 

Among  Fucoidece  sexual  reproduction  is  known  in  only  a  few 
cases.  Much  is  yet  to  be  discovered,  though  in  some  respects  our 
knowledge  concerning  the  comparative  significance  of  the  phe- 
nomena of  reproduction  is  quite  exact.  The  difference  in  the 
phenomena  of  reproduction  in  Fucoidece  and  Floridece  may  be 
readily  explained  from  a  teleological  standpoint.  The  spermato- 
zoids  of  Fucoideoe  have  cilia,  therefore  possess  autonomous  move- 
ment, while  the  fertilizing  elements  of  Floridece  (red  marine  algge) 
are  without  cilia,  and  hence  motionless,  and  are  called  ' '  spermatia ' ' 
(o  nepua,  seed).  In  perfect  harmony  with  such  facts  we  find  that 
the  egg- cell  of  Fucoidece  is  first  set  free  and  is  endowed  with 
autonomous  movement,  and  may  be  reached  by  the  equally  free 
swimming  spermatozoids.  Among  Floridece  fertilization  is  accom- 
plished by  the  female  organ  ("  carpogone  ")  sending  out  a  hair- 
like  structure  ("  trichogyne  ")  from  the  fixed  egg-cell  to  which 
the  spermatia  become  attached.  Floridece  also  reproduce  asexually 
by  means  of  ' '  tetraspores ' ' ;  these  are  formed  by  each  mother- 
cell  dividing  into  four  parts  (BORNET,  THURET,  PRINGSHEIM,  and 
others). 

B.   FORMS  OF  REPRODUCTION  AMONG  FUNGI. 

The  following  is  a  brief  summary  of  the  chief  forms  of  repro- 
duction among  the  fungi.  Asexual  reproduction  predominates. 
The  asexual  spores  are  produced  either  endogenously  or  exoge- 
nously.  When  exogenous,  either  basipetally  or  acropetally  on  the 
basidia  or  immediately  on  the  mycelium.  (The  exogenous  spores 
are  sometimes  called  oonidia  in  distinction  to  the  endogenously  pro- 
duced endospores.) 

We  will  first  mention  the  two  groups  Zygomycetes  and  Oomy- 
cetes  in  which  sexual  reproduction  usually  occurs.  As  the  names 
would  indicate,  we  have  conjugation  with  the  formation  of  zygo- 
spores  in  the  former  group,  and  oospore-formation  in  the  latter 
group.  In  the  genus  Mucor  endospore-formation  also  occurs, 
("mould"  on  bread,  fruit,  old  damp  clothing,  leather,  etc.,  be- 
longs to  Mucor.)  Finally,  we  will  mention  BREFELD'S  chlamy do- 
spore-formation  as  an  asexual  mode  of  reproduction.  By  this  is 


REPROD  UCTION. 


195 


understood  a  ' '  secondary  morphological  change ' '  caused  by  some 
checking  influence  on  the  development  of  the  sporangiophores, 
which  then  assume  the  function  of  spores.  In  a  book  of  this  kind 
it  is  well  to  adhere  to  facts  obtained  from  actual  observation,  and 
not  to  enter  into  too  many  speculative  considerations. 

Among  the  Oomycetes  there  occurs  reproduction  by  means  of 
•conidia  and  swarm-spores,  besides  the  formation  of  oospores,  men- 


FIG.  118. — Achlya  lignicola. 
(After  Sachs.) 


FIG.  119.— Formation  of 

swarm-spores  in  AcJdya. 

(After  Sachs.) 


tioned  above.  As  an  example  we  may  mention  Achlya  lignicola 
as  one  species  of  a  group  of  fungi  found  upon  dead  flies  and  other 
insects,  in  water,  etc.  Fig.  118  (A-E)  shows  the  oospore-forma- 
tion.  Fig.  119  shows  the  swarm-spore  formation.  The  fungus 
Phytophthora  infestans,  which  also  belongs  to  this  group,  and 
which  is  so  destructive  to  the  potato-plant,  has  no  sexual  repro- 


196 


COMPENDIUM  OF  GENERAL  BOTANY. 


ductive  organs,  at  least  none  have  so  far  been  observed.     It  has 

very  minute  characteristic  conidial 

J 
spores. 

We  shall  now  discuss  the 
numerous  fungi  which  have  only 
asexual  reproduction,  namely,  the 
Ascomycetes,  J3asidiomycetes,  Ure- 
dvnece,  and  Ustilaginece.  The 
differences  in  reproduction  as  ex- 
pressed in  the  names  of  the  first 
two  groups  are  illustrated  in  Figs, 
120  and  121. 

FIG.  120--Asc^^ores'  of  Peziza        Within  the    two    large  groups 
(After  Berthoid  and  Landois.)  Ascomycetes    and    Bdsiclwmycetes 

there  is  in  each  a  sub-group  without  a  sporocarp  or  covering  for 
the  spore-bearing  tissue;  the  remaining  sub-groups  have  sporo- 
carps.  In  regard  to  the  two  genera  Polyporus  and  Agaricus,  it 
is  to  be  observed  that  they  represent  the  essential  differences  be- 
tween the  Agaricinei  and  Polyporei  ;  the  lamellae  (gills)  in  the  one 
and  the  pores  in  the  other  are  simply  different  arrangements  of  the 


Fig.  121.  Fig.  122. 

FIG  121  and  FIG.  122.— Gills  (lamellae)  from  the  lower  surface  of  a  toad-stool. 
a,  Moderately  enlarged;  6,  basidium^^^^^  magnified.)  122,  Lamt 

hyphal  tissue  especially  adapted  to  give  rise  to  spore-producing 
basidia.  The  following  terms  apply  to  the  reproductive  organs  of 
many  Basidiomycetes :  peridium,  gleba,  and  capillitium.  The 
first'is  the  covering  which  encloses  the  entire  spore-bearing  tissue 
of  the  Gasteromycetes.  Gleba  is  the  inner  hyphal  tissue  enclosed 
'  by  the  peridium.  This  hyphal  tissue  contains  pores  or  chambers; 
the  walls  of  these  pores  are  called  trama,  and  are  lined  with 


REPRODUCTION. 


197 


spores.  The  spores  are  set  free  by  the  rupturing  of  the  peridium, 
while  the  cells  of  the  trama  enter  into  dissolution,  except  certain 
colls  which  form  a  loose  network  of  hyphal  filaments,  the  capil- 
litium. 

The  Ustilaginece  (blights)  and  Uredinece  (rusts)  form  either 
single  terminal  spores  or  chains  of  spores.  Among  the  UredinecB 
occurs  a  peculiar  phenomenon  called  ' '  heteroecie ' '  (change  of  host) 
by  its  discoverer,  DE  BARY.  Successive  generations  live  upon 
different  substrata,  in  this  case  upon  different  living  plants  (para- 
sitic). Heteroecie  is  known  in  about  fifty  species  of  rusts.  The 
names  ' '  blight ' '  and  ' '  rust ' '  already  indicate  that  we  are  con- 
cerned with  plant-diseases.  We  will  first  discuss  the  hetercecious 
rust-fungi,  then  the  blight-fungi. 

Puccinia  graminis,  the  rust  of  our  grasses,  especially  grains, 
is  far  more  injurious  than  the  blight-disease.  Blight  is  limited  to 
single  plants  of  our  cereals,  while  rust  appears  epidemically  by  its 
rapidly  formed  and  germinating  summer-spores.  The  methods  of 
exterminating  this  plant-disease  are  as  follows :  1.  To  destroy  the 
4 '  intermediate ' '  host,  which  serves  as  a  substratum  for  one  genera- 
tion :  in  Puccinia  straminis  the  jBorraginece,  and  in  Puccinia 
graminis  the  shrub  Berberis  vulgaris  (see  Fig.  123).  2.  To  de- 


FIG.  123.—  A,  Young  aecidium  ;  /«,  mature  aecidia  (a)  on  a  lenf-sectiou  of  Berberis 
vulgaris  ;  B,  highly  magnified  telentospore  of  Puccinia  graminis. 


(After  Sachs.) 

stroy  as  many  as  possible  of  those  plants  which  shelter  the  teleuto- 
spores  during  the  winter  months,  that  is,  the  remnants  left  in  the 


198  COMPENDIUM  OF  GENERAL  BOTANY. 

grain-fields.  3.  Grasses  growing  wild  in  the  grain-fields  (example  : 
Triticum  repens)  often  serve  as  hosts  to  the  fungus.  These  must 
also  be  destroyed. 

The  course  of  development  in  Puccinia  graminis  is  as  follows : 
(a)  The  fungus  lives  upon  the  leaves  of  Berberis  vulgaris  during 
the  spring  and  produces  seeidiospores  (Fig.  123,  7&,  A),  which 
are  carried  to  the  wheat-  or  oat-plants  by  the  wind ;  (&)  germina- 
tion and  growth  begin  at  once  and  end  with  the  formation  of 
uredospores,  which  may  be  carried  to  other  plants  and  also  develop. 
(The  spermagonia  and  spermatia  shown  in  Fig.  123,  sp,  are  little 
understood.  Formerly  they  were  supposed  to  be  male  sexual 
organs.1)  The  earlier  che  fungus  attacks  the  plants  the  more  in- 
jurious are  the  effects.  Sometimes  all  the  leaves  are  infected,  even 
the  glumes.  Toward  the  close  of  the  vegetative  period  (<?)  teleuto- 
spores  are  formed,  which  remain  at  rest  during  the  winter  months 
and  begin  to  germinate  in  the  early  spring.  From  them  grows  (d) 
&promycelium  with  sporidia.  The  sporidia  develop  upon  suitable 
hosts  (in  this  case  upon  the  leaves  of  Berberis)  and  again  form 
secidiospores,  thus  forming  the  beginning  of  a  new  cycle  of 
development. 

Tilletia  Caries  causes  the  smut  of  wheat;  various  species  of 
Ustilago  cause  the  blight  of  different  grasses,  especially  of  oats, 
barley,  and  wheat.  (To  prevent  the  occurrence  of  both  of  these 
fungi  it  is  necessary  to  soak  the  seed  to  be  sown  in  a  J  per  cent 
solution  of  sulphate  of  copper  for  about  twelve  or  fourteen  hours 
and  then  to  sow  the  seed  during  dry  weather.)  In  this  disease 
spore-formation  takes  place  in  the  ovarium  with  destruction  of  the 
ovulum,  while  the  assimilating  organs  (leaves  and  stems)  are  not 
attacked,  as  in  rust-diseases.  The  spores  adhere  to  the  outside  of 
the  seed ;  hence  it  is  advisable  to  soak  it  in  a  copper-sulphate  solu- 
tion of  sufficient  strength  to  destroy  the  spores  without  destroying 
the  germinating  powers  of  the  seed.  The  group  of  fungi  to  which 
Tilletia  belongs  develops  conidia  upon  basidia  which  are  peculiar 
in  that  they  arrange  themselves  in  the  form  of  an  II  before  develop- 
ing into  a  mycelium,  which  again  produces  rust-spores. 

In  conclusion  we  wrill  mention  reproduction  in  a  fungus  from 
the  group  of  Ascomycetes,  namely,  Clavipes  purpurea,  usually 

1  See  foot-notes  on  pp.  189  and  200  in  reference  to  spermagonia  of  lichens. — 
TRANS. 


REPRODUCTION.  199 

known  as  sclerotium  in  its  resting  stage.  This  plant  has  potent 
medicinal  properties.  In  its  general  outline  the  sclerotium  takes 
on  the  form  of  the  rye-grain  which  it  attacks ;  it  is  usually  larger 
and  somewhat  curved.  It  consists  of  a  closely  woven  network  of 
hyphal  filaments  (mycelium)  forming  a  firm  semi-cortical  structure, 
brown  externally  and  white  internally.  Infection  takes  place  as  fol- 
lows :  The  surface  of  the  young  rye-ovary  is  covered  by  a  mycelial 
network  (honey-dew)  which  also  penetrates  the  interior.  Conidia 
are  formed  on  the  exterior.  This  conidia-forming  network  was 
formerly  known  as  Sphacelium,  and  was  supposed  to  be  a  dis- 
tinct fungus.  Near  the  base  of  this  structure  the  mycelium  of  the 
sclerotium  begins  to  form ;  this  develops  rapidly  and  in  its  mature 
state  bears  the  remnants  of  the  sphacelium  and  the  rye- ovary  on 
its  apex.  The  sclerotium  is  a  "  pseudo -parenchyma,"  that  is,  the 
hyplise  of  the  fungus  are  so  closely  interwoven  that  they  resemble 
a  parenchymatous  tissue.  (Such  pseudo-parenchymatous  tissues  are 
also  met  with  among  lichens.)  The  conidia,  which  are  formed 
when  the  rye  is  in  blossom,  constitute  the  first  means  of  propagation 
and  spreading  from  seed  to  seed.  The  sclerotium,  which  lies 
dormant  during  the  winter  months,  develops  elongated  spores  in 
the  spring.  These  spores  (ascospores)  constitute  the  second  form 
of  reproductive  cells  of  this  fungus.  Under  favorable  conditions 
the  ascospores  may  develop  in  the  fall,  but  the  sclerotinm  is  specially 
adapted  to  withstand  the  vicissitudes  of  the  winter  season,  so  that 
its  spores  may  develop  into  the  sphacelium -stage  during  the  follow- 
ing spring.  Preventative  measures  :  Since  this  fungus  is  in  great 
demand  by  druggists  (even  imported  from  America),  it  will  pay 
doubly  to  collect  the  sclerotia  before  the  grain  ripens.1  In  the 
second  place  non-infected  seed-grain  must  be  selected.  It  is  also 
well  to  destroy  such  grasses  as  Lolium  perenne,  which  frequently 
spreads  the  fungous  disease. 

Reproduction  among  lichens2  is  the  same  as  in  that  group  of 
fungi  which  constitutes  the  fungal  symbiont  in  the  lichen-structure. 
In  the  great  majority  of  lichens  the  fungal  portion  is  derived  from 
the  Aseomycetes,  a  few  genera  from  the  Basidiomycetes.  They 
also  reproduce  by  means  of  vegetative  organs,  the  soredia,  which 

1  It  might  be  mentioned  that  such  a  procedure  would  scarcely  be  successful 
in  the  large  grain-fields  of  America. — TRANS. 

2  Their  structure  was  briefly  discussed  under  Symbiosis. 


200  COMPENDIUM  OF  GENERAL  BOTANY. 

are  formed  in  great  numbers  upon  the  lichen-thallus  and  are  carried 
long  distances  by  the  wind.  These  soredia  contain  loth  constitu- 
ents of  the  lichen-body,  alga  and  fungus.  For  certain  Ascoliehenes 
STAHL  has  very  probably  demonstrated  the  existence  of  sexual 
reproduction. ' 


II.  A  COMPARATIVE  STUDY  OF  REPRODUCTION  AND 
ALTERNATION  OF  GENERATION  IN  MOSSES,  VAS- 
CULAR CRYPTOGAMS,  AND  PHANEROGAMS. 

Comparative  morphology  shows  certain  analogies  occurring  in 
the  course  of  development  in  the  above-named  great  groups  of 
plants.  Considering  this  fact  from  the  standpoint  of  the  doctrine 
of  creation  does  not  reveal  anything  surprising.  It  rather  confirms 
and  elucidates  the  workings  of  that  uniform  idea  which  called  into 
life  and  controlled  the  great  series  of  vegetable  organisms.  The 
intellectual  work  which  disclosed  these  analogies  appears  the  more 
gigantic  since  the  resemblances  are  often  indistinct,  or  on  the  other 
hand  the  actual  differences  between  the  various  groups  to  be  com- 
pared are  often  very  abrupt.  HOFMEISTER  must  be  credited  with 
first  having  revealed  these  analogies.  Human  intellect  has  received 
the  ability  to  comprehend  the  Creative  Idea  within  a  certain  limit. 
The  fact  that  the  stated  differences  or  boundary-lines  between  the 
great  divisions  of  plants  are  intellectual,  that  is,  can  only  be 
bridged  over  by  processes  of  thought,  decides  in  favor  of  our  con- 
ception of  the  subject.  Concrete  connecting  links  as  they  are  sup- 
posed to  exist  by  the  believers  in  natural  descent  cannot  be  demon- 
strated. Although  our  conception  of  this  subject-matter  differs 
from  that  of  the  prevailing  tendency  in  the  wider  scientific  circles, 
yet  we  maintain  that  our  process  of  reasoning  is  founded  upon  a 
purely  scientific  basis.  The  existence  of  points  of  similarity  not- 
withstanding evident  contrasts  indicates  the  ruling  of  a  uniform 


'  Recently  STURGIS  has  apparently  verified  STAHL'S  observations.  In  some 
instances  the  supposed  male  sexual  organs  (sperinatia  of  Stahl)  are  very  likely 
spores  of  a  parasitic  fungus  (spermagoue  of  Stahl)  living  upon  the  lichen.  Further 
investigation  is  necessary. 

(It  should  be  noted  also  that  the  most  recent  writers  on  lichenology  (REINKE) 
consider  lichens  ns  autonomous,  having  a  phytogeny  of  their  own,  and  should 
therefore  be  considered  as  a  distinct  class.— TRANS.) 


REPRODUCTION.  201 

idea;  only  the  speculative  fantasy  of  the  theory  of  descent  finds 
it  necessary  to  construct  concrete  connecting  links  between  these 
existing  contrasts. 

In  regard  to  the  differences  just  mentioned,  the  following  shall 
now  be  mentioned,  although  the  beginner  will  only  comprehend  the 
subject  fully  from  what  will  be  stated  later. 

1.  No  pollen -grain  of  a  phanerogamic  plant  is  capable  of  pro- 
ducing motile  spermatozoids,  while  on  the  other  hand  no  micro- 
spore  of  a  vascular  cryptogam  can  develop  a  pollen-tube. 

2.  By  comparing  the  phanerogams  with  viviparous  animals,  as 
Sachs  has  done,  we  find  that  the  contrast  between  vascular  crypto- 
gams and  phanerogams  is  too  great  to  enable  us  to  compare  the 
vascular  cryptogams  with  oviparous  animals.      This  fact  Sachs  him- 
self emphasized. ' 

3.  Although  the  antheridia  and  archegonia  of  vascular  crypto- 
gams and  leafy  mosses  resemble  each  other,  it  is  evident  that  the 
relative  behavior  of  sexual  and  asexual  generation  is  materially 
different.     Among  mosses  the  leafy  plant  develops  from  spores 
produced  asexually,  while  among  vascular   cryptogams  the    plant 
proper  is  the   product  of  the  fertilized  egg- cell.       NAGELI,    the 
shrewdest  and  most  zealous  supporter  of  the  theory  of  descent, 
supposes  that  the  present  phanerogams  were  derived  from  former, 
now  extinct,  vascular  cryptogams,  and  these  from  moss-like  plants.2 

We  shall  now  enter  more  fully  into  the  particulars  of  this  com- 
parative study.  Let  us  suppose  the  entire  development  of  a  plant, 
beginning  with  a  reproductive  cell  and  terminating  with  a  cell  of 
equal  value,  to  be  represented  upon  a  circle,  as  is  shown  in  the 
accompanying  diagramatic  sketch  (Fig.  124,  1,  2).  This  shows 


FIG.  124. 

the  relation  between  a  moss  and  a  fern.     1  Represents  the  moss 
and  2  the  fern ;    G  the  sexual  generation  and  U  the  asexual  genera- 


1  Vorlesungeu,  p.  922. 

2  Mech.-phys.  Theorie  der  Abstauirnimgslehre,  p.  472. 


202 


COMPENDIUM  OF  GENERAL  BOTANY. 


tion.  Among  mosses  the  sexual  generation  (Gr)  is  prominent,  it 
forms  the  independent  green  plant ;  the  asexual  generation  ( U\ 
which  forms  asexual  spores,  does  not  even  have  an  independent 
existence ;  it  exists,  so  to  speak,  as  a  parasite  upon  the  leafy  moss- 
plant  forming  the  sporogonium  (moss-capsule,  spore-fruit). 
Among  vascular  cryptogams  the  large  leafy  plant  constitutes  the 
asexual  generation,  while  the  minute  green,  short-lived  structure 
called  \hQprothallium,  represents  the  sexual  generation  upon  which 
the  archegonia  and  anther idia  are  formed. 

In  regard  to  the  structure  of  the  sporangium  of  mosses,  I  wTill 
state  that  the  capsule  of  most  liverworts  contains  spores  in  the 
internal  axial  space,  while  in  the  leafy  mosses  the  spore-bearing 

area  takes  a  more  periphe- 
ral position,  that  is,  between 
the  sterile  central  column 
(columella)  and  the  wall  of 
the  capsule.  For  the  present 


FIG.    125    T.  —  Funaria     liygrometrica. 

Three  stages  of  the  developing  sporogonium 
(//');  bb,  ventral  portion,  h,  neck,  of  sporo- 
gonium. The  base  (bb)  forms  the  calyptra 
c(C).  (A  X  500,  B  and  O  X  40.)  (After  Sachs.) 


FIG.    125    II.  —  Funaria    hygro- 
metrica. 

A,  Shoot  bearing  an  immature  sporo- 
gonium, 0,  with  calyj)tra  c,  upon 
the  capsule.  B,  Nearly  mature  sporo- 
gonium; /,  capsule  with  calyptra  c; 
s,  seta  (stem).  C,  Longitudinal  sec- 
tion of  sporogonium;  cc',  columella; 
s,  spore-forming  layer;  /i,  air-cavity; 
a,  the  ring  (annulus)  below  the  lid 
(operculum);  p,  "peristome."  (After 
Sachs.) 


we  will    omit   further   particulars.      Figs.  125  I  and  125  II,   as 


REPRODUCTION. 


203 


FIG.  126. 
Adiantum  capillus-veneris.    (After  Sachs.) 


well  as  those  already  referred  to,  will  assist  in  further  elucidating 

these  relations. 

A  fern-prothallmm  with 

a    young   sporophytic   fern- 
plant  is  shown  in  Fig.  126. 

This  young  plant  is  the  result 

of    the    fertilization   of   the 

archegonium.       The  root  is 

seen  at  t0,  the  first  leaf  at  b. 

We  will  now  compare  vascular  cryptogams  and  phanerogams 

(Fig.  127,  1  and  2).     The  ruled  rectangle  represents  the  period  of 

separation  from  the  mother- plant  and  winter-rest ;  S  represents  the 

asexually  produced  ma- 
crospore  and  the  embryo- 
sac;  E  is  the  egg-cell. 
$  Represents  the  micro- 
spore  in  1  and  the  pollen- 
grain  in  2. 

The  beginner  will  be 
surprised  to  learn  that 
the  entire  phanerogamic 
plant  with  its  flowers  rep- 
resents the  asexual  genera- 
tion. If  this  be  so,  where 
is  the  sexual  generation  ? 
Its  existence  is  limited  to 
a  minimum  of  space  and 
time.  In  its  behavior  it 
is  markedly  different  from 
the  corresponding  genera- 
tion in  the  vascular  cryp- 
togams. Let  us  consider 
that  which  is  analogous 
and  that  which  is  not  an- 
alogous. The  embryo- 
sac  and  the  pollen -grain 
are  indeed  represented  by 
analogous  structures  in 

the   vascular  cryptogams;    such   analogies   are   the   most   marked 


204  COMPENDIUM  OF  GENERAL  BOTANY. 

in  the  c '  heterosporous  ' '  cryptogams,  whose  sexually  different  spores 
have  different  prothallia.  The  larger  spores,  macrospores,  produce 
the  archegonia,  corresponding  to  the  embryo-sac  and  egg-cell.  The 
smaller  spores,  mwrospores,  produce  the  fertilizing  element,  similar 
to  the  pollen-tube  of  pollen.  Let  us  now  consider  the  differences. 
The  macrospore  becomes  separated  from  the  mother-plant  and  for 
a  time  leads  an  independent  existence  during  which  it  germinates 
and  produces  archegonia.  The  embryo-sac  of  gymnosperms,  of  the 
phanerogams  in  particular,  remains  in  union  with  the  mother-plant. 
It  is  enclosed  by  the  coverings  of  the  ovule,  which  usually  appear 
as  the  parts  of  a  peculiarly  modified  leaf.  The  entire  ovule  as  well 
as  the  perfected  pollen-grain  are  structurally  arranged  so  that  the 
egg-cell  in  the  embryo-sac  may  be  formed  and  fertilized  while  still 
in  union  with  the  mother-plant.  After  fertilization  the  eg^-cell 

J-  oo 

undergoes  division  and  develops  into  the  embryo  of  the  future  plant. 
Both  the  embryo-sac  and  macrospore  possess  sufficient  reserve  food- 
material  to  make  the  formation  of  the  embryo  possible.  When 
the  embryo  is  fully  formed,  it  becomes  separated  from  the  mother- 
plant  and  after  a  period  of  rest  germinates  and  develops  into  a  new 
plant.  It  is  possible  to  distinguish  a  neck  and  a  basal  portion  of 
the  so-called  u  archegonium  "  of  gymnosperms,  as  in  the  arche- 
gonium  of  ferns. 

The  microspore  is  separated  from  the  mother-plant,  likewise  its 
equivalent,  the  pollen-grain.  However,  the  "  germinating ' '  micro- 
spore  of  Selaginella,  a  vascular  cryptogam,  produces  an  entirely 
different  structure  from  that  produced  by  the  germinating  pollen- 
grain,  although  there  is  a  marked  external  similarity.  In  vascular 
cryptogams  fertilization  takes  place  in  water ;  motile  spermatozoids 
with  spirally  wound  plasmic  cilia  are  formed.  The  pollen-tube,  a 
single  non-septate  slender  filament,  is  formed  from  the  pollen-grain. 
Air-currents,  insects,  etc.,  carry  the  pollen-grain  to  the  moist 
stigma  of  the  pistil,  where  it  germinates,  sending  out  the  above- 
mentioned  pollen -tube,  which  penetrates  the  soft  tissues  of  the 
stigma  and  style,  finally  reaching  the  cavity  of  the  ovary,  where  it 
enters  through  the  openings  in  the  seed-coats  (mi'cropylar  opening) ; 
here  it  comes  in  contact  with  the  apex  of  the  body  of  the  ovnle  and 
embryo-sac,  and  finally  the  egg-cell.  The  morphological  appearance 
of  the  developing  pollen-tube  is  wholly  different  from  the  develop- 
ment of  the  microspore.  Their  internal  structure,  which  is  also 


REPRODUCTION.  205 

wholly  different,  we  will  not  discuss.  Neither  a  supporter  of  the 
theory  of  descent  nor  any  physiologist  can  at  the  present  time  hope 
to  solve  the  question — What  changes  are  necessary  in  the  idioplas- 
matic  structure  in  order  that  a  microspore  which  regularly  forms 
motile  fertilizing  elements  may  develop  a  fertilizing  tube  like  that 
of  the  pollen -grain? 

The  so-called  ' '  vegetative ' '  cells  which  regularly  appear  in  the 
pollen -grains  of  conifers  are  looked  upon  as  evidence  in  favor  of 
the  theory  of  descent.  These  pollen-grains  are  several-celled,  but 
only  one  cell  develops  into  the  pollen-tube.  The  remaining  cells 
are  supposed  to  be  a  "  rudimentary  male  prothallium. ' '  The 
microspore  of  Selaginella  is  also  several-celled,  and  has  a  vegetative 
cell.  Anxious  searchers  for  phylogenetic  characters  will  naturally 
allow  themselves  to  become  blinded  by  factors  apparently  in  their 
favor.  Even  in  the  present  state  of  our  knowledge  on  the  subject 
I  will  venture  the  statement  that  the  contents  of  the  vegetative 
cells  in  the  pollen-grains  of  conifers,  etc. ,  serve  to  nourish  the  cell 
which  develops  into  the  pollen-tube.  According  to  JUEANYI,  one 
of  the  vegetative  cells  contains  starch.1  ELFVING*  states  that  the 
vegetative  cell  of  Leucoium  oestivum  is  reabsorbed,  while  its  nucleus 
as  well  as  the  nucleus  of  the  reproductive  cell  is  later  found  in 
the  pollen-tube.  Other  observations  teach  that  very  long  cells, 
such  as  the  laticiferous  tubes  and  the  bast-cells,  are  frequently 
multinuclear.  It  must  also  be  remembered  that  the  pollen-grain 
of  conifers  requires  a  long  time  to  reach  its  destination,  hence  must 
have  some  food-supply. 

In  Selaginella,  which  contains  two  kinds  of  spores,  the  macro- 
spore  separates  from  the  mother-plant  before  the  formation  of  the 
archegonia.  The  germinating  macrospore  which  develops  sterile 
archegonia  is  not  equivalent  to  the  germinating  seeds  of  phanero- 
gams, but  rather  to  the  embryo-sac,  which  is  not  adapted  to  become 
separated  from  the  mother-plant,  hence  does  not  separate,  and 
forms  its  egg-cell  apparatus  near  the  apex,  in  the  most  suitable 
location  for  fertilization.  From  the  above  considerations  of  re- 
production we  see  that  that  which  is  physiologically  equivalent  may 
differ  very  widely  morphologically.  The  ripe  seed  of  phanerogams 


1  Pringsheim's  Jabrbucber,  VIII,  1872. 

2  Studieu  ilber  die  Pollenkoraer,  etc.,  Jeu.  Zeitscbrift  f.  Naturwissenschaft, 
XIII  (new  series). 


206  COMPENDIUM  OF  GENERAL  BOTANY. 

will  at  once  develop  into  a  leafy  plant  while  the  mature  macrospore 
must  be  fertilized  before  it  can  develop  into  a  new  plant ;  from 
this  it  is  clear  that  structures  which  resemble  each  other  morpho- 
logically1 may  be  totally  different  physiologically.  The  names 
macrospore  and  microspore,  embryo-sac  and  pollen-grain,  should 
therefore  be  retained  as  parallel  terms.  If  one  purposely  ignores 
what  has  just  been  stated,  especially  that  among  vascular  crypto- 
gams the  sequence  is  separation  from  the  mother-plant  and  sub- 
sequent fertilization,  while  the  reverse  is  true  of  gymnosperms,  it 
can  be  seen  how  the  advocates  of  the  theory  of  natural  descent  can 
assert  that  the  gymnosperms  may  be  classed  with  the  vascular  crypto- 
gams as  well  as  with  the  phanerogams,2  that  is,  that  they  are  midway 
between  the  two  great  divisions. 

Because  of  the  importance  of  this  subject  we  will  add  the  fol- 
lowing statements. 

From  what  has  been  said  it  would  be  wrong  to  conclude  that  a 
slight  change  in  the  behavior  of  the  macrospore  would  suffice  to 
prove  the  phylogenetic  derivation  of  gymnosperms  from  the  vascular 
cryptogams.  Let  us  consider  briefly  what  these  changes  would  be 
and  what  changes  should  not  take  place.  In  order  that  Selaginella 
may  arrive  at  the  cycad-stage  the  macrospore  must  not  adapt  itself 
to  become  separated  from  the  mother-plant  nor  undergo  a  period 
of  rest  until  it  has  been  fertilized  by  the  suitably  organized  micro- 
spore.  After  this  change  had  been  brought  about  separation  from 
the  mother-plant  could  follow,  and  the  disposition  to  undergo  a 
period  of  rest  should  now  become  manifest.  In  order  that  the 
macrospore  might  remain  in  union  with  the  mother-plant  it  must 
undergo  an  entirely  different  mode  of  development.  What  slight 
similarity  exists  between  the  Cycas-ovule  and  the  sporangium  of 
Selaginella  is  evident  from  GOBEL'S  statement  that  the  integument 
of  the  Cycas-embryo  has  no  analogue  among  vascular  cryptogams, 
and  therefore  he  calls  it  a  ' '  neo-f  ormation. ' '  This  investigator  is  cer- 

c? 

tainly  authority  on  subjects  pertaining  to  comparative  morphology. 
The  macrospores  of  the  Cycas- sporangium  are  not  formed  by  the 
mother-cell  dividing  into  four,  as  in  the  Selaginella.  In  regard  to 


1  It  should  be  remembered  that  such  morphological  similarity  or  dissimilarity 
of  organs  which  seem  dissimilar  or  similar  physiologically  is  often  only  apparent, 
and  not  real. — TRANS. 

2  SACHS,  Vorlesungen,  p.  913;   GOBEL,  Grundzilge  der  Systematik,  p.  1. 


REPRODUCTION. 


207 


the  cuticularization  of  the  outermost  layer  of  the  wall  of  the  em- 
bryo-sac, it  may  be  said  that  it  is  of  importance  in  the  processes  of 
nutrition,  as  is  evident  from  my  investigations  in  regard  to  the 
* '  antipodal ' '  cells.  It  aids  in  conducting  food-materials  along 
definite  paths.  It  has  not  been  demonstrated  that  such  cuticular- 
ization owes  its  origin  to  ' '  phylogeny . ' ' 

I  will  close  this  discussion  with  the  following  statement :  If  the 
great  gulf  between  vascular  cryptogams  and  gymnosperms  did  not 
exist,  it  would  not  have  been  necessary  for  the  genius  of  HOF- 
MEISTER  (in  1851)  to  introduce  a  tertium  comparationis  in  the 
great  plant-groups,  the  vascular  cryptogams  and  gymnosperms. 

It  is  now  necessary  to  explain  some  of  the  special  adaptations 
for  reproduction  and  development  among  the  vascular  cryptogams. 

The  sporangia  of  vascular  cryptogams  usually  occur  in  small 
groups  (sori)  upon  the  lower  surface  of  the  leaf,  or  as  shield-like 
organs  on  supports,  as  in  Equisetince.  Up  to  the  time  of  maturity 
these  sporangia  are  usually  covered  by  a  protective  organ,  the 
indusium,  or  more  rarely  by  the  curled  margin  of  the  leaf.  The 
sporangia  contain  the  spores.  In  the  mature  sporangia  of  many 
ferns  (Fig.  128)  there  is  noticeable  an  incomplete  median  ring  of 


FIG.  128.—  Aspidium  Filix  mas. 

A,  Vertical  section  of  a  sorus  &s  with  indusium  t;  J?,  pinnule  with  sori;  C,  single  immature 
sporangium;  d,  glandular  hair.    (After  Sachs.) 

thickened  cells.     By  a  sudden  mechanical  movement  (hygroscopic 
movement)  this  ring  aids  in  ejecting  the  spores. 


208 


COMPENDIUM  OF  GENERAL  BOTANY. 


In  Fig.  128,  (7,  it  is  noticeable  that  the  ring  extends  from  r  at 
the  left  of  the  base  of  sporangium  to  r  at  the  right.  The  cells  of  this 
ring,  when  mature,  are  considerably  thickened  along  the  inner  side, 
as  well  as  in  the  radial  direction  (vertical  to  the  surface  of  the 
figure). 

Fig.  129  shows  the  product  of  the  fertilized  archegonium. 
The  egg-cell  has  developed  into  a  young  plant  with  leaf,  stem,  and 
root  (5,  s,  w).  The  foot  (f)  of  the  embryo  absorbs  the  food-mate- 
rial (starch)  of  the  spore  at  c ;  i  is  the  inner,  ex  the  outer,  spore- 
membrane  (exospore).  The  prothallium  pt  shows  the  root-hairs 


FIG.  129. — Macrospore  with  prothallium  FIG.  130. — Longitudinal  sec- 

and  embryo  of  Marsilia  salvatrix.  tion    through   the   tip  of  a 

(X  60.)   (After  Sachs.)  fertile  branch  of  Selaginella 

incequalifoUa. 

(After  Sachs.) 

wh,  and  the  mucous  covering  si  which  aids  the  spermatozoids  in 
reaching  the  egg-cell ;  the  root-hairs  serve  as  a  temporary  attach- 
ment to  the  soil  at  the  bottom  of  the  water.  Fig.  130  shows  a 


REPRODUCTION. 


209 


fertile  branch  of  Selaginella  incBqicalifolia^  with  macrosporangia 
and  inicrosporangia. 

Finally,  in  reference  to  what  has  been  stated  and  what  remains 
to  be  considered,  we  will  add  the  following  in  explanation  of  the 
diagramatic  figures  (131  and  132).  Both  refer  to  the  phanerogams. 
In  the  figure  (129)  of  Marsilia  and  that  of  gymnosperms  (131) 
we  at  once  notice  the  provision  made  for  the  nourishment  of  the 
embryo.  The  embryo  is  entirely  surrounded  and  connected  with 
the  nutritive  tissue,  the  endosperm.  Fig.  132  represents  the  pro- 
cess of  fertilization  among 
angiosperms.  In  Marsilia 
and  the  gymnosperms  the 
endosperm  exists  before 
fertilization,  while  in  the 
angiosperms  it  is  formed 
after  fertilization.  Recent 
investigations  by  the  author 1 
resulted  in  the  probable  con- 
clusion that  the  ' '  antipodal 
apparatus ' '  which  exists 
before  fertilization  is  not  a 
' c  rudimentary ' '  organ,  but 
a  peculiar  structural  arrange- 
ment to  serve  in  nourishing 
the  developing  embryo. 
Until  recently  the  antipodal 
cells  were  considered  as 
being  without  any  physio- 
logical function,  but  of  suf- 
ficient value  to  indicate  a 
' '  phy logenetic  rudiment. ' ' 
As  indicated,  the  subject  is 
perhaps  capable  of  an  en-  Fm  131._Diagramatic  longitudinal  section 
tirelv  different  interpreta-  through  the  ovule  of  a  gymuosperm. 

"    mi  fa   T     •  (After  Sachs.) 

tion .    There  are  cases  (8ama 

pratensis,  Zea  Mays)  in  which  the  so-called  antipodes  prove  to  be 

1  Zur  Embryologie  der  Phanerogamen,  insbesoudere  liber  die  sogenanuten 
"  Antipodeu."  Nova  Acta  d.  Ksrl  Leop.  Car.  D.  Ac.  d.  Naturf.  1890  (The  Em- 
bryology of  Phanerogams,  with  special  reference  to  the  so  called  "Antipodes"). 


210 


COMPENDIUM  OF  GENERAL  BOTANY. 


the  primordial  endosperm-cells,  since  they  unite  with  the  remain- 
ing endosperm  immediately  after  fertilization.     (For  further  par- 


PIG.  132. — Diagramatic  longitudinal  section  through  the  flower  of  an  angiosperm. 

(After  Sachs.) 

ticulars  refer  to  the  work  cited  below.)  In  conclusion  I  will  add 
that  the  antipodes  also  indicate  a  nutritive  function  by  their  position 
and  arrangement. 


GYMNOSPEEMS  AND  ANGIOSPERMS. 

As  is  well  known,  the  phanerogams  are  divided  into  the  great 
groups  yymnosperms  and  angiosperms. 

What  has  already  been  said,  especially  in  reference  to  the  above 
diagramatic  figure  (131),  will  aid  in  understanding  the  following 


REPRODUCTION.  211 

particulars  in  regard  to  the  process  of  fertilization  among  gymno- 
sperms.  A  pollen-grain  (h)  is  carried  by  the  wind  to  the  opening 
left  in  the  integument  of  the  embryo,  namely,  the  micropylar 
opening  (&).  This  is  made  possible  by  the  position  of  the  ovules  at 
the  inner  side  of  the  base  of  the  seminiferous  scale,  as  shown  in 
Fig.  133.  The  scales  mutually  cover  and  protect  each  other,  yet 
the  pollen-grains  may  get  between  them  at  certain  times.  At  first 
the  pollen-grain  is  found  near  the  upper  part  of  the  seminiferous 
scale  adhering  to  a  sticky  fluid  which  is  secreted  at  this  time. 
This  fluid  is  carried  downward,  and  with  it  the  pollen-grain.  Soon 
the  pollen-tube  begins  to  form  and  passes  through  the  nucellus  (b  &), 
finally  reaching  the  archegonia.  (The  time  intervening  between 
pollination  and  fertilization  is  an  entire  year  for  many  gymno- 
sperms.) e  and  e'  (Fig.  131)  show  the  immediate  results  of  fertil- 
ization. In  e'  the  egg- cell  of  the  archegonium  has  developed  into 
a  filamentous  structure  (/"),  the  "  suspensor,"  on  the  end  of  which 
the  embryo  is  formed.  The  suspensor  serves  to  push  the  embryo 
into  the  endosperm.  The  structure  of  the  archegonia,  as  well  as 
the  fact  that  the  embryo-sac  is  filled  with  endosperm  before  fertil- 
ization, places  the  gymnosperms  nearer  to  the  vascular  cryptogams 
than  to  the  angiosperms.  Such  a  relative  position  cannot  be  denied, 
but  the  recognition  of  such  a  relation  is  simply  a  process  of  thought 
wrhich  the  comparative  study  of  the  plant-series  creates  in  our 
minds ;  that  such  a  series  is  genetic  is  an  unverified  postulate  of  the 
dogmatic  teaching  of  descent  which  allows  fantasy  to  supplant 
that  which  empirical  investigations  leave  unanswered. 

As  has  already  been  observed,  the  embryo  of  gymnosperms  is 
not  unprotected,  as  the  name  would  indicate.  Among  pines  and 
firs,  for  example,  the  leaf-organs  which  bear  the  ovules,  hence  the 
4 '  carpides  "  or  "  carpels, ' '  are  enabled  by  their  position  and  ar- 
rangement to  cover  each  other.  The 
morphological  significance  of  the  cone- 
scales  was  formerly  the  cause  of  con- 
siderable scientific  controversy.  A 
small  leaf -scale  (keel)  supports  the 
much  larger  seminiferous  scale  as  a 
ventral  excrescence.  In  Fig.  ^^ 
A,  d  represents  the  leaf -scale;  the 
large  seminiferous  scale  in  B  bears  the  ovules  b  5,  which  later  form. 


212  COMPENDIUM  OF  GENERAL  BOTANY. 

the  ripe  seeds  variously  equipped  with  winged  appendages  for  the 
purpose  of  facilitating  their  distribution  by  air-currents.  EICHLER 
for  a  long  time  considered  the  seminiferous  scale  as  a  "  meta- 
morphosed shoot."  The  entire  cone  would  therefore  be  the  in- 
florescence. Now  the  entire  structure  is  considered  to  be  a  single 
female  flower,  which  bears  numerous  peculiarly  modified  seed-leaves- 
on  one  axis.  STRASBURGER  made  a  special  study  of  conifers. 

We  will  here  note  that  the  stem-structure  and  the  mode  of 
axillary  branching  represent  further  differences  between  conifers 
and  angiosperms.  Concerning  the  differences  between  the  male 
flowers  of  gymnosperms  and  angiosperms  we  will  give  further  par- 
ticulars in  the  discussion  of  stamens. 

In  distinction  to  gymnosperms  the  ovule  of  angiosperms  is  usually 
situated  at  the  margin  of  the  carpel ;  the  latter  organ  is  not  flat, 
but  typically  arched,  forming  a  hollow  structure  (the  ovary).  This 
organ  may  be  formed  from  a  single  carpel  or  by  the  adhesion 
(growing  together)  of  several  carpels.  These  several  carpels  are  so 
united  that  the  ovules  inserted  in  the  margins  come  to  lie  in  the 
interior  of  the  cavity  so  formed.  The  united  margins  on  which 
the  ovules  are  inserted  are  known  as  placentae.  This  adhesion  of 
parts,  which  does  not  exist  in  gymnosperms,  because  it  is  not 
required,  necessitates  still  other  structural  adaptations  for  the  pur- 
poses of  pollination  and  fertilization.  Since  the  ovary  is  closed, 
the  pollen  cannot  be  brought  to  the  micropyle  by  the  wind  or  in- 
sects. There  is  a  special  organ,  the  stigma  (Fig.  132,  A),  which 
receives  the  pollen-grain ;  also  a  second  organ,  the  style  (g),  which 
forms  the  path  for  the  growing  pollen-tube  (k  I  m).  The  seed- 
leaves  (carpels)  by  their  union  form  a  longer  or  shorter  canal  at  the 
upper  part  known  as  the  stylar  duct  (Griffelkanal).  This  channel, 
which  is  either  hollow  or  composed  of  soft  tissue,  is  bounded  above 
by  the  papillose  terminations  of  the  carpellary  leaves,  which  con- 
stitute the  stigma.  These  terminations  may  differ  greatly  morpho- 
logically ;  they  may  appear  as  fine  rays,  papillae,  etc.  The  stigma 
secretes  a  moist  sticky  substance  to  which  the  pollen-grains  adhere 
and  in  which  they  begin  to  germinate.  The  pollen-tube  extends 
down  the  stylar  duct  into  the  cavity  of  the  ovary ;  special  structural 
adaptations  may  also  exist  for  conducting  the  growing  pollen-tube 
to  the  micropylar  opening.  In  reference  to  the  explanation  of  Fig. 
132  the  following  is  added:  a,  transverse  section  of  anther;  £r 


RE  PROD  UCTION.  213 

longitudinal  section  ;  <?,  filament ;  /,  wall  of  ovary ;  n,  the  fum'cu- 
lus ;  o,  base  of  the  embryo ;  p  and  <?,  outer  and  inner  integument ; 
«?,  nucellus;  t,  embryo-sac;  v,  and  s,  egg-cell  apparatus  (syner- 
gida?);  u,  antipodes;  e,  nectaries;  d,  basal  portion  of  the  floral 
envelopes. 

For  the  time  being  we  will  discontinue  the  discussion  of  the 
further  processes  and  products  of  fertilization;  they  will  be  re- 
ferred to  at  the  close  of  III  and  in  chapter  IY  of  this  section. 
We  shall  now  take  up  the  consideration  of  the  general  morphology 
and  physiology  of  the  phanerogamic  flower. 

III.    THE  PHANEROGAMIC   FLOWER. 

Although  the  c  c  moss-flower  ' '  has  both  sexual  organs  upon  the 
same  axis,  it  is  not  analogous  to  the  hermaphroditic  flower  of 
phanerogams,  which  also  bears  carpels  and  stamens  on  one  axis. 
We  know  from  what  has  already  been  stated  that  the  spores  of  the 
moss- sporangium  have  an  origin  analogous  to  that  of  the  embryo-sao 
and  the  pollen-grains.  The  formation  of  the  germinal  vesicle  in 
the  embryo- sac,  and  the  divisions  and  other  processes  which  prepare 
the  pollen -grain  for  germination,  correspond  to  the  sexual  genera- 
tion represented  by  the  development  of  the  leafy  moss-plant. 

We  will  now  make  a  comparative  study  of  the  following 
phanerogamic  flowers:  (1)  the  female  flower  of  a  pine,  Picea 
excelsa-;  (2)  the  flower  of  rye,  Secale  cereale  ;  (3)  the  hyacinth, 
Hyacinthus  orientalis  ;  (4)  the  cherry-flower,  Prunus  Cerasus. 

Number  1  represents  the  gymnospermous  flowers;  2  repre- 
sents not  only  the  gramineous  flower,  but  all  monocotyledonous 
flowers  with  colorless  corollas ;  Hyacinthus  is  an  example  illustrat- 
ing the  apetalous  monocotyledonous  and  dicotyledonous  flower. 
Finally,  Prunus  Cerasus  represents  the  type  of  the  apparently 
* '  most  perfect ' '  flower,  equipped  with  calyx,  corolla,  stamens, 
and  carpels  (pistils). 

In  the  discussion  of  leaf -organs  (Part  III,  B,  2)  the  floral  leaves 
were  very  briefly  touched  upon.  We  shall  now  enter  into  a  more 
thorough  discussion.  By  introducing  physiological  factors  we  will 
be  able  to  overcome  the  disagreeableness  of  mere  dry  description. 


214  COMPENDIUM  OF  GENERAL  BOTANY 


A.  CALYX,  COROLLA,  NECTARIES.     THE  FLOWER  AS  A  WHOLE. 

In  Picea  excelsa  the  ovules  are  protected  by  the  overlapping 
of  the  cone- scales.  We  have  learned  that  the  torus  with  the  style 
and  stigma  is  not  necessary  in  this  case.  Because  of  the  firmness 
and  arrangement  of  these  scales  no  calyx  is  necessary  (among  $ 
flowers  bud- scales  protect  the  stamens).  Since  fertilization  is 
brought  about  by  the  wind,  a  colored  corolla  is  also  unnecessary — 
the  color  serves  to  attract  insects ;  the  nectaries  are  likewise  absent, 
their  function  being  to  attract  insects.  Petals  are  also  absent  from 
number  2.  In  numbers  3  and  4  they  are  present,  because  hya- 
cinths and  cherry-flowers,  as  well  as  thousands  of  other  colored 
flowers,  are  dependent  upon  insects  for  pollination.  The  con- 
ditions of  reproduction  in  spite  of  hermaphroditism  (in  2,  3,  and  4) 
are  so  regulated  that  the  great  majority  of  hermaphroditic  or  bi- 
sexual flowers  are  dependent  upon  cross-fertilization.  In  only  a 
very  small  number  of  cases  has  it  been  found  that  self -fertilization 
is  more  beneficial. 

The  pine  (1)  is  dioecious.  Since  the  wind  is  the  means 
by  which  pollination  is  brought  about  (anemophilous),  it  is  evident 
that  pollen  must  be  very  plentiful  to  insure 
fertilization ;  this  we  find  to  be  the  case. 
Sometimes  pollen-grains  possess  vesicular  en- 
largements of  the  exine  which  facilitate  their 
distribution  by  the  wind  (Fig.  134,  bl). 

In    the    anemophilous    Graminece    (2)    the 
FIG.  134.-Pollen  grain 
of  Pinus  Pinaster.      pollen-grams  are  caught  and  retained  by  the 

(After  Sachs.)  delicate  bristles  of  the  stigma  (see  Fig.   135). 

The  small  scales  at  the  base  of  the  stamens,  the  so-called  ' '  lodic- 
ulse, ' '  have  a  mechanical  function ;  by  swelling  they  assist  in  open- 
ing the  flower.  At  least  they  need  not  be  considered  as  forming  a 
' '  rudimentary ' '  perianth  or  calyx,  since  the  bracts  or  glumes 
take  the  place  of  the  calyx.  As  a  rule,  each  individual  flo\ver  has 
two  secondary  bracts  (palece)  and  each  spikelet  has  two  primary 
bracts  (glumes).  It  would  be  wholly  wrong  to  suppose  that  the 
flower  of  the  conifers  or  grasses  is  rudimentary  or  imperfect  as 
compared  with  the  flower  of  the  cherry-tree. 

Numbers    3   and  4  represent   types  of   flowers   whose   pollen 


REPRODUCTION. 


215 


_ 

FIG.  135.—  Spikelet  of  rye  with 
two  flowers. 


three  stamens  and  the  pistil. 


is  carried  to  the  stigmas  of  other  plants  of  the  same  species,  and 
they  in  return  receive  pollen  from  other  plants.  The  transfer  is 
made  by  insects,  and  such  flowers  are 
said  to  be  entomophilous.  The  petals 
of  the  corolla  are  either  united  or  free 
in  the  different  groups  of  angiosperms. 
They  often  have  peculiar  adaptations 
of  form  to  facilitate  the  fertilization 
by  insects.  Different  odors,  sometimes 
pleasant  and  sometimes  very  disagree 
able,  as  well  as  various  glandular  secre- 
tions (nectaries)  serve  a  to  attract  insects. 
Why  the  organ  known  as  calyx, 

which  may  consist  of  either  separate  or 

J 
united  sepals,  is  absent  in  number  2  has 

already  been  explained.     In  Hyacinthns 
there   is   no  differentiation   into   calyx 

-,  IT  T.-,      -.      ,-,  ,     . 

and  corolla,  while  both  are  present  in 
Prunus  (4.  See  Fig.  138).  The  calyx  by  its  position  and  greater 
firmness  protects  the  younger  and  more  delicate  parts  of  the  flower. 
It  would,  of  course,  be  functionless  if  other  organs  were  adapted  to 
perform  this  protective  function.  There  is  besides  Hyacinthus  a  large 
series  of  monocotyledon  ous  flowers  in  which  the  calyx  is  normally 
absent.  Floral  coverings  which  consist  of  equal  or  nearly  equal  leaf- 
like  organs  without  any  distinction  as  to  calyx  and  corolla  are  known 
as  i\\Q  perianth.  In  its  appearance  it  may  resemble  either  the  calyx 
or  corolla.  It  is  remarkable  that  these  '  '  apetalous  '  '  monocotyle- 
dons (orchids,  aroids,  onions)  are  equipped  with  larger  or  smaller 
hypsophyllary  leaves  in  the  axils  of  which  the  young  individual 
flower  (orchids)  or  the  young  inflorescence  (aroids,  onions)  finds  a 
suitable  protection.  Further,  it  is  noticeable  that  among  many  of 
the  apetalous  flowers  the  rather  firm  perianth-leaves  are  green  at 
first  and  enclose  the  flower-bud;  later  they  unfold  and  take  on 
bright  colors.  In  the  first  stage  they  resemble  the  calyx  in  appear- 
ance and  function  ;  in  the  second  stage  they  resemble  more  nearly 
the  corolla.  In  Fritillaria  imperialis,  a  plant  belonging  to  the 
same  group  as  3,  special  organs  occur  at  the  base  of  the  perianth- 
leaves  which  secrete  a  saccharine  liquid  ;  they  are  known  as  nec- 
taries and  are  found  in  various  flowers.  Their  function  has  already 


216  COMPENDIUM  OF  GENERAL  BOTANY. 

been  mentioned,  but  will  again  be  referred  to  in  the  discussion  of 
cross-fertilization. 

From  the  foregoing  we  may  conclude  that  there  are  parts  of 
the  flower  which  serve  the  function  of  reproduction  directly,  and 
parts  which  aid  indirectly.  To  the  first  belong  the  gynwcium  and 
the  androecium,  that  is,  the  male  and  female  sexual  organs  of  the 
flower.  The  calyx,  the  corolla,  the  perianth,  the  nectaries,  and 
the  hypsophyllary  leaves  aid  reproduction  indirectly,  since  these 
organs  may  be  substituted  for  one  or  the  other  of  the  inessential 
organs.  The  flowers  of  the  pine  require  no  calyx,  no  corolla, 
no  nectaries,  or  torus.  All  such  structures  would  be  without  a 
purpose.  The  flowers  of  grasses  require  no  calyx,'  corolla,  or 
nectaries,  as  their  absence  indicates.  A  monocotyledonous  flower 
with  a  perianth,  as  the  hyacinth,  may  also  be  without  calyx. 
Flowers  of  Prunus  as  well  as  those  of  many  other  phanerogamic 
plants  require  calyx,  corolla,  and  nectaries  for  the  purposes  of  re- 
production, as  is  indicated  by  their  presence.  Nature  does  not  pro- 
duce any  useless  structures. 

Number,  form,  and  arrangement  of  floral  organs  and  their  parts 
play  a  very  important  role  in  the  morphology  of  flowers  and  in  the 
classification  of  plants.  What  LINNE  so  fortunately  considered  to 
be  of  importance  in  establishing  his  system  of  phanerogams  is 
embodied  in  its  essentials  in  our  present  system  of  classification ; 
that  is,  the  recognition  of  constant  floral  characteristics,  such  as 
number,  cohesion  of  parts,  size,  symmetry,  etc.  The  following  is 
a  brief  summary  of  such  characteristics. 

If  the  calyx,    corolla,  stamens,  and  pistils  succeed  each  other 
vertically  on  one  axis  (receptacle  or  torus),  we  have  what  is  known 
as  a  Jiypogynous  flower.      The  ovary  is  said  to 
be  superior  (Fig.  136). 

In  the  second  case  (Fig.  137)  the  develop- 
ment of  the  floral  axis  is  such  that  the  apex 
FIG.  136.— Hypogyncms  appears   depressed,  that  is,  a  peripheral  wall 
flower     (Ranuncula-  rises  above  the   apex,   so  that  in  the  mature 

fP(P\ 

(After  Berthoid  and  Lan-  structure  the  ovary  with  its  ovules  lies  below 
the  base  of  the  insertion  of  the  stamens  and 
petals.      Such    a    flower    is  said    to    be     epigynous  j    ovary    in- 
ferior. 

Finally,  in  the  third  case  (Fig.  (138)  the  stamens  and  petals 


REPROD  UCTION.  217 

surround  the  ovary.  Such  a  flower  is  said  to  be  perigynous. 
The  floral  axis  is  also  depressed,  but  the  ovary  differs  from  case 
2  in  that  it  is  "  free. ' '  In  the  case  of  epigyny ,  according  to 
GOBEL'S  investigations,  the  cup-shaped  floral  axis  is  lined  on  its 
inner  surface  by  the  basal  parts  of  the  floral  envelopes.  These 


FIG.  137. — Epigy  nous  flower  FIG.  138. — Perigynous  flower  (cherry). 

(apple).  ('After  Berthold  and  Landois.) 

(After  Berthold  and  Landois.) 

floral  envelopes  have  a  strong  intercalary  growth,  soon  enveloping 
the  ovary,  with  the  exception  of  the  terminal  portions  of  the  styles 
and  stigma.  In  the  perigynous  flower  the  intercalary  growth  of 
the  cup- shaped  axis  is  perhaps  a  little  below  the  insertions  of  the 
floral  coverings,  that  is,  the  floral  insertions  are  so  near  the  apex 
of  the  torus  that  they  are  not  affected  by  the  intercalary  growth ; 
hence  the  torus  is  not  enclosed  by  the  floral  coverings.  Forms 
intermediate  between  epigyny  and  perigyny  are  not  wanting. 

The  individual  parts  of  the  flower  may  be  free  or  united  / 
sometimes  the  organs  are  free  below  and  united  (by  growth)  above, 
as,  for  example,  the  stamens  of  the  Composite.  The  number  of 
floral  parts  differs  greatly  in  different  flowers.  For  example,  the 
stameniferous  flower  of  Euphorbia  has  but  one  stamen,  while  the 
flowers  of  the  NympJiaeece,  may  have  more  than  one  hundred. 

The  number  three  prevails  in  the  floral  elements  of  monocoty- 
ledons. The  numbers  vary  among  dicotyledons,  though  fives  are 
very  common. 

According  to  the  arrangement  of  floral  leaves  we  may  recognize 
the  following  forms  of  flowers. 

1.    Cyclic  flowers:    the  elements  of  one  kind  of  floral  leaves 


218 


COMPENDIUM  OF  GENERAL  BOTANY. 


are  in  the  same  horizontal  plane,  "verticillate."     Example:  the 
Isiliiflorce. 

2.  Acyclic  flowers:    spiral    arrangement   of   the  floral  leaves. 
Example :  Magnolia. 

3.  Ilemicydic  flowers :   the  floral  organs  may  in  part  be  spirally 
arranged  (especially  the  calyx)  and  in  part  verticillate.     Example : 
JRanunculacece. 

The  calyx  usually  forms  one  circle  of  floral  leaves;  the  corolla 
also  one ;  the  androecium  one  or  two ;  the  gyncecium  usually  one. 
For  causes  more  or  less  associated  with  the  mechan- 
ical theory  of  phyllotaxy  there  is  often  noticeable 
an  alternate  arrangement  of  members  of  the  vari- 
ous verticillse,  provided  they  occur  in  equal  num- 
bers (see  Fig.  139).  The  whorls  or  verticillae  may 
also  be  opposite,  as  shown  in  Fig.  140. 

A  further  discussion  of  these  relations  would 
soon  lead  us  to  that  stage  of  investigation  in  which 
the  comparative  morphology  of  flowers  seems  to 
give  evidence  of  the  transmutation  of  one  genus  into  another. 
We  will  cite  an  example.  Normally  the  Scrofulariacece  have  five 
stamens;  Veronica  has  two;  Gratiola  has  two 
normal  stamens  and  two  sterile  structures,  the  so- 
called  ' '  staminodia. ' '  Digitalis  and  Scrofidaria 
have  four  stamens  and  one  staminodium.  It  is 
evident  that  the  abortion  or  the  suppression  of  stamens 
plays  an  important  part  in  the  cases  mentioned.  By 


FIG.  139.—  Dia- 
gram  of  the 
flower  of  Lili- 


Krass   and 
Landois.) 


this  ' '  suppression ' ' 


FIG.    140.— Dia- 
gram   of    the 
is  meant  the  non-appearance  of      flowerofPnw- 

an  organ  which  one  would  expect  to  appear  accord-  (AJjf*'  Krass  and 
ing  to  reasons  deduced  from  comparative  morphology.         Landois.) 
In  some  cases  an  entire  whorl  may  be  suppressed  or  fail  to  appear. 
In  other  cases  there  is  not  a  suppression  of  members,  but  an  increase 
in  the  normal  number  of  parts  ("  dedoublement  "). 

Since  SCHUMANN'  has  applied  SCHWENDENER'S  contact  theory  to 
the  processes  of  growth  and  development  in  the  floral  region  of 
the  plant  the  investigations  in  regard  to  this  subject  have  been 
placed  upon  a  firmer  foundation,  while  the  play  of  fancy  is  to  a  cer- 
tain extent  checked.  The  exact  history  of  development,  the  study 


1  Neue  Untersuchungen  liber  den  Bltiteuanschluss,  Leipzig,  Engelmann,  1890. 


REPRODUCTION.  219 

of  which  is  in  every  case  a  difficult  and  tedious  work,  teaches  that, 
for  example,  the  first  primordia  (protuberances)  are  acted  upon  by 
various  mechanical  influences  which  give  rise  to  superposed  whorls. 
I  have  no  cause  to  enter  into  a  discussion  of  the  conditions  met 
with  in  the  flowers  of  Scrofularia,  because  I  do  not  know  any 
more  about  the  origin  of  this  genus  than  any  one  else  does. 

Before  entering  into  the  discussion  of  the  important  relations  of 
the  floral  structure  it  is  important  to  remember  that  the  great 
variety  represented  in  the  structure  of  flowers  and  fruits  can  no 
longer  be  relegated  to  mere  description,  but  must  be  considered 
according  to  physiological  adaptations.  Although  this  change  in 
our  science  is  comparatively  recent,  we  are  already  enabled  to  give 
physiological  interpretations  to  many  of  the  structural  modifica- 
tions ;  always  from  a  teleological  standpoint.  The  purpose  of  many 
of  these  modifications  is  to  insure  the  most  suitable  pollination  and 
fertilization.  Under  this  category  belong  the  following  structural 
modifications. 

A  flower  is  said  to  be  poly 'symmetrical  or  actinomorphio  when 
it  may  be  symmetrically  divided  in  at  least  two  planes.  (Slight 
differences  are  not  considered.)  Illustration:  the  diagram  (Fig. 
139)  of  Lilium.  A  flower  is  zygomorphic  or  symmetrical  when 
it  can  be  divided  symmetrically  in  only  one  plane.  Sometimes 
there  is  no  plane  of  symmetry,  when  the  flower  is  said  to  be 
azygomorphic.  The  diagram  of  the  labiate  flower  is  an  excel- 
lent example  of  a  zygomorphic  flower  (Fig.  142).  The  zygo- 
morphic flowers  are  nearly  always  lateral.  If  a  plant  with  zygo- 
morphic flowers  should  huve  a  terminal  flower,  it  is  actinomorphic. 
(Linaria  vulgaris  frequently  shows  this  phenomenon.  Such  ter- 
minal flowers  are  said  to  be  peloric. J ) 

The  plane  of  symmetry  of  zygomorphic  flowers  usually,  but 
not  always  (Solanum,  ^Esculus),  coincides  with  the  median  plane. 
The  majority  of  flowers  are  therefore  median-zygomorphic.  The 
median  plane  is  that  plane  which  bisects  the  axis  of  growth  of  a 
lateral  member  as  well  as  the  axial  member.  Only  a  few  flowers 
are  transversely  zygomorphic ;  that  is,  the  plane  of  symmetry  and 
the  median  plane  form  an  angle.  In  many  orchid-flowers  the 
ovary  or  style  rotates  about  its  axis  180°,  which  brings  the  young 

1  Lateral  peloric  flowers  are  also  reported.     Whether  such  lateral  position  is  real 
or  only  apparent  I  am  unable  to  state. — TRANS. 


220 


COMPENDIUM  OF  GENERAL  BOTANY. 


zygomorphic  flower  in  a  suitable  position  to  be  visited  by  insects. 
Fig.  141  illustrates  the  phenomenon  of  "resupination."  The 
above-mentioned  labiates  show  this  zygomorphy  in  a  marked  degree 
in  the  two-lipped  calyx  and  corolla  (Figs.  142  and  143).  This 


FIG.  141. — Orchis  fusca. 

(After  Berthold  and  Landois. ) 


FIG.  142.— Dia- 
gram of  a  la- 
biate flower. 

(After    Krass   and 
Landois.) 


FIG.  143. — SaMa  pratensis. 
a,  Anthers;  b.  pistil. 


PIG.  144.  —  Dia- 
gram of  apapilio- 
naceous  flower. 

(After       Krass     and 
Landois.) 


FIG.  145.— Dia- 
gram of  *a  cru- 
ciferousflower. 

(After    Krass    and 
Landois.) 


FIG.  146.—  Centaurea  cyanus. 
(After  Krass  and  Landois.) 


family,  which  comprises  about  2600  species,  is  widely  distributed 
(EICHLEE).  The  Papilionacece  comprise  about  3000  species 
(Eichler) ;  their  floral  arrangement  is  represented  diagramatically 
in  Fig.  144. 

The  Liliaceve  represent  the  actinomorphic  type.  Of  the  dicoty- 
ledons we  shall  refer  to  the  Cruciferce  (Fig.  145),  comprising  about 
1200  species  (Eichler)  and  distributed  throughout  the  temperate 
zones. 


REPRODUCTION. 


221 


Among  the  Umbelliferce  as  well  as  the  Composite  the  flowers  of 
the  same  inflorescence  (umbel,  head)  are  often  different ;  the  central 
ones  are  actinomorphic  and  the  peripheral  ones  zygomorphic. 
Among  the  Composites  there  are  distinct  strap-shaped  and  tubular 
flowers,  or  even  two-lipped  flowers,  in  place  of  the  former.  Fig. 
146,  &,  shows  the  involucre  of  hypsophyllary  leaves ;  m,  a  tubular 
bisexual  flower;  /•,  a  sterile  two-lipped  marginal  flower;  J,  the 
receptacle;  M,  a  hypsophyllary  leaf;  f,  ovary;  <?,  style  with 
stigma;  sf  and  sb,  filaments  with  united  anthers.  The  Umbelliferce 
are  distributed  through  the  temperate  zone  and  comprise  about 


FIG.  147.— Aethusa  cynapium. 
a,  Umbel;  c,  flower;  e,  fruit;  /,  cross-section  of  the  fruit;  g,  leaf.    (After  Krass  and  Landois.) 

1300  species  (Eichler).     Figs.  147-149  are  given  to  represent  the 
general  characteristics  of  this  family. 

The  dicotyledons  are  now  usually  divided  into  Choripeialoe  and 


222  COMPENDIUM  OF  GENERAL  BOTANY. 

Sympetalce,  according   to  whether  the  petals  of  the    corolla    are 

free  or  united.  To 
the  former  belong 
the  CrucifercB, 
Ranunculaceoe,  and 
fiosacece;  to  the 
latter  the  Ldbiatce, 

FIG.      149.  —  Carum   Gentianacece,  Sola- 
carvi.    Diagramatic  ~ 

cross-section    of    a  ncwew,      Composite®. 


148,-Seed     of     Daneu.  61 


, 

Carola  (carrot).  oil-glands  near  6  and  e\    ceminS"        "  SVmpet- 

(After  Berthold  and  Landois.)  d  and  ''  Primary  ribs;  e  O  J 

secondary  ribs  with  oil-    alollg  '  '   flowers.) 

(A"En!]o^er)th°ld  and  We  will  now 

consider  the  structure  and  function  of  the  nectaries,  and  then  pass 
to  the  discussion  of  the  andrcecium  and  gyncecium. 

As  already  indicated,  the  nectaries  serve  to  secrete  a  honey-like 
substance  called  nectar.  This  secretion  attracts  insects,  which  feed 
upon  it,  and  by  their  movements  on  lighting  and  attempting  to 
secure  the  nectar  cause  the  pollen  to  adhere  and  alight  upon  them, 
to  be  carried  to  other  plants  (of  the  same*  species)  for  the  purposes 
of  cross-fertilization.  The  nectaries  are  morphologically  different 
in  different  plants.  In  Alchemilla  vulgaris  they  are  located  in 
the  calyx,  very  frequently  they  are  located  in  the  petals,  forming 
the  spurs  of  orchids,  Ranunculacece,  etc.  In  Caltha  palustris 
they  are  located  near  the  base  of  the  ovary  ;  in  Cerastium,  near  the 
base  of  the  filament  ;  among  many  of  the  Liliacece  they  occur  in 
the  septa  of  the  ovaries,  and  are  known  as  septal  glands.  Finally, 
there  are  nectaries  formed  by  special  structural  modifications,  such 
as  those  of  Parnassia  palustris  and  Musa  paradisiacal 

Not  every  insect  can  secure  the  nectar  of  any  flower.  Certain 
insects  are  especially  adapted  to  certain  flowers  in  order  to  bring 
about  cross-fertilization.  The  depth  of  the  floral  tube  and  the  spur 
corresponds  to  the  length  of  the  proboscis  of  the  visiting  insect. 
There  are  also  protective  arrangements  to  prevent  the  visit  of  use- 
less or  harmful  insects.  Such  are  the  hair-cells  and  scaly  structures 
in  the  corolla,  which  sometimes  makes  access  to  nectaries  difficult  or 
impossible  (Labiatce,  Asperifolice)  ;  also  the  so-called  *  '  masked  '  ' 

1  Studied  more  in  particular   by  W.  BEHRENS,  Flora,  1879.     The  above  state- 
ments are  based  upon  the  investigations  of  this  author. 


REPRODUCTION.  223 

corollas,  in  which  the  hood  of  the  lower  lip  is  closely  appressed  to  the 
upper  lip  (Linaria).  ANTON  v.  KEENER,  who  lias  made  a  special 
study  of  alpine  plant-life,  has  added  to  botanical  literature  two 
important  volumes,  entitled  ' '  Protective  Arrangement  of  the  Pollen 
against  Premature  Liberation  and  Germination,"  and  u  The  Pro- 
tection of  Flowers  against  Undesirable  Guests."  In  reference  to 
the  latter  work  (Innsbruck,  1 879),  I  will  state  that  it  was  above  all 
the  author's  desire  to  show  clearly  the  suitable  adaptations  of  the 
various  floral  arrangements  and  to  strengthen  our  teleological  con- 
ception of  nature.  We  do  not  see  in  it  any  evidence  in  support  of 
the  theory  of  selection,  as  the  author  seemed  to  indicate  in  the  in- 
troduction to  this  work.  CH.  K.  SPRENGEL  (1793)  made  important 
discoveries  in  regard  to  the  physiological  significance  of  individual 
floral  parts,  especially  the  corolla  and  its  zygomorphy.  He  is  the 
discoverer  of  the  law  of  the  absence  of  self-fertilization.  We  now 
know  that  this  ' '  law  ' '  is  not  generally  applicable,  since  there  are 
plants  with  special  adaptations  for  self-fertilization  (see  below, 
cleistogamous  flowers). 

.     *• 

B.   THE  STAMENS  AND  POLLEN-GRAINS. 

The  stamens  of  gymnosperms  are  in  general  quite  different 
from  those  of  angiosperms.  In  the  former  the  part  which  bears 
the  pollen-sacs  is  sometimes  flat,  sometimes  peltate  or  cylindrical ; 
in  the  angiosperms  it  is  in  general  filamentous,  and  is  known  as 
the  filament.  Among  gymnosperms  the  number  of  pollen-sacs  is 
usually  much  greater  and  more  variable  than  among  angiosperms; 
two  is  the  usual  number  in  the  latter  group. 

The  following  discussion  of  stamens  is  based  upon  their  ap- 
pearance among  angiosperms.  To  explain  the  structure  and 
function  of  this  organ  we  will  give  the  important  characteristics 
illustrated  by  a  few  typical  examples. 

The  elongated  portion,  filament,  supports  the  anthers  (pollen- 
sacs).  Fig.  150  shows  the  most  frequent  form  of  dehiscence  or 
opening  of  the  anther,  that  is,  it  splits  open  in  its  longitudinal 
direction ;  more  rarely  there  are  pores  formed  at  the  apex,  or  the 
apices  may  open  by  means  of  transverse  valves.  In  the  Ericaceae 
we  find  an  interesting  arrangement.  The  anthers  open  by  the 
formation  of  pores.  The  hardened  appendages  of  the  anthers 


224 


COMPENDIUM  OF  GENERAL  BOTANY. 


assist  in  the  expulsion  of  the  pollen-grains  when  insects  come  in 
contact  with  them.     (See  Fig.  152.) 

Let  us  now  consider  the  anther  in  cross-section — represented 
considerably  magnified  in  Fig.  153,  A,  B.  A  represents  the 
cross-section  of  an  entire  anther,  in  which  the  valves  have  separated 
from  the  pillar  (connective  tissue)  at  z.  B  is  the  very  highly  mag- 
nified portion  /3 ;  e  is  the  epidermis  and  x  the  fibrous  mechanical 
layer.  At  $/,  B,  it  can  be  plainly  seen  that  the  fibrous  layer  does 
not  extend  quite  to  the  pillar.  Anatomically  this  is  the  weakest 
point,  and  at  which  separation  takes  place.  The  middle  portion 
in  A  in  which  the  vascular  bundle  lies  is  called  the  connective, 


FIG.  150.  FIG.  152. 

FIG.  150.—  Anther  of  white  lily. 

a  and  6,  Modes  of  dehiscence.    (After  Berthold  and  Landois.) 
FlG.   151.  —  Cross-section  of  an  anther      (After  Berthold  and  Landois  ) 
FIG.  152.  —  Longitudinal  section  through  the  pistil  and  two  anthers  of  Calluna 

(After  Berthold  and  Landois  ) 


because  it  serves  as  a  union  between  the  two  parts  of  the  anther. 
Each  half  may  also  possess  two  chambers  ;  the  entire  anther  is 
therefore  either  two-  or  /bw/'-chambered.  If  one  supposes  the 
four  chambers  to  be  close  together  on  one  side  of  the  connective 
we  have  an  anther  with  both  longitudinal  openings  on  one  side. 
If  the  dehiscence  is  inward  (in  reference  to  the  ilower)  the  an- 
thers are  designated  as  being  introrse  ;  if  facing  outward,  they  are 
said  to  be  extrorse.  A  teleological  relation  which  has  been  studied 
more  in  particular  by  JORDAN  '  is  of  special  importance.  The 
position  of  the  nectaries  is  dependent  upon  introrsity  and  extrorsity, 


Die  Stellung  der  Honigbebalter  etc.     Dissertation.     Halle,  1886. 


REPRODUCTION. 


225 


and  other  relations  of  the  anthers.  It  need,  of  course,  not  be 
stated  that  insects  perform  the  act  of  pollination  of  plants  uncon- 
sciously. The  place  where  they  are  engaged  in  securing  honey  is 


FIG.  153. — Cross-sections  of  an  anther.     (After  Sachs.) 


The 


also  the  appropriate  place  to  come  in  contact  with  pollen, 
following  is  from  Jordan's  communication. 

1.  Anthers  introrse.     Nectaries  intrastaminal,  that  is,  between 
the  androecium  and  the  gynoecium ;  as  in  Dianthus  Carthusiano- 
rum.  Lychnis  dioica,  Nymphcea  alba,  Oomarum  palustra,  Allium 
Schcenoprasum,  etc. 

2.  Anthers   extrorse.     Nectaries   extrastaminal,   that   is,    be- 
tween the  androecium  and  the  corolla  or  between  corolla  and  calyx ; 
as  in  Ranunculus  acer,  Tilia  grandifolia,  Parnassia  palustris, 
etc. 

Most  interesting  are  those  cases  in  which  the  anthers  appear  to 
be  unsuitably  related  to  the  nectaries  as,  for  example,  in  Convolvu- 
lus arvensis.  We  cannot  take  time  to  discuss  these  relations. 
(Compare  Fig.  143.) 

We  will  now  pass  from  the  forms  of  dehiscence  to  the  mecha- 
nism of  dehiscence.  The  important  factor  is  the  anatomical  struc- 
ture of  the  anther- wall  (Fig.  153,  B\  The  epidermis  does  not 
assist  materially  in  the  opening  of  the  anther,  the  fibrous  layer  (x) 
(endothecium)  is  looked  upon  as  the  mechanically  active  tissue. 
As  has  already  been  stated,  the  weakest  point  is  where  the  two 
valves  are  attached  to  the  pillar  of  the  connective.  Thin- walled 
cells  form  the  connecting  tissue.  The  question  arises,  Whence  the 
tension  which  causes  the  margins  of  the  valves  to  separate  from  the 
connective?  We  can  actually  observe  a  shortening  of  the  fibrous 
layer  (in  the  mature  anther)  during  gradual  drying,  so  that  the  wall 
curls  back.  Let  us  consider  the  individual  cell  of  the  fibrous  layer 


226 


COMPENDIUM  OF  GENERAL  BOTANY. 


or  endothecium.  It  is  supplied  on  its  inner  wall  and  on  the  radial 
walls j  as  seen  in  cross-section,  with  thickened  bands  which  project, 
inward.  The  outer  wall  in  contact  with  the  epidermis  does  not  *] 
contain  these  thickenings.  These  bands  extend  at  right  angles  to 
the  epidermis  on  the  radial  walls,  those  of  the  inner  walls  extend 
in  all  directions.  The  result  of  this  thickening  is  that  on  drying 
the  radial  walls  contract  much  more  rapidly  in  the  tangential  direc- 
tion than  do  the  inner  walls.  The  thickenings  in  the  radial  walls  act 
as  levers,  exerting  a  force  outwardly,  but  not  inwardly.  The  ten- 
dency to  shorten,  which  is  manifest  in  the,  radial  walls,  is  neutral- 
ized as  soon  as  the  margins  of  the  valves  become  separated  from 
the  pillar  of  the  connective.  The  opening  and  recurving  of  the 
valves  is  a  very  sudden  explosive  act,  whereby  the  pollen-grains  are 
thrown  out  with  considerable  force.  In  the  sporangium  of  ferns 
the  weakest  point  corresponds  to  the  group  of  thin-walled  cells 
terminating  the  annulus.  The  latter  is  also  the  outermost  cell- 
layer  (see  Fig.  128,  C).  The  radial 
walls  of  the  annulus  lying  parallel  to 
the  plane  of  the  ring,  as  well  as  the 
outer  walls,  are  thin;  the  remaining 
radial  walls  and  the  inner  walls  are 
thick.  The  cause  for  the  immediate 
opening  of  the  annulus  (sporangium)  is 
the  same  as  in  the  anther,  only  that  in 
the  sporangium  the  evaporation  of  moist- 
ure is  very  rapid,  since  it  can  pass  at 
once  to  the  atmosphere  through  the  thin 
outer  walls  of  the  cells.1 

Returning  to  the  structure  of  an- 
thers, we  must  not  forget  to  mention 
that  in  anthers  which   open    by  pores 
the  fibrous  layer  is  entirely  absent,  since 
they    do   not    require   any    mechanism 
opening     (Ericaceae,     Pirolacece, 
(After  Sachs.)  MelastomacecB) . 

The  pollen-grains  are   isolated  cells   or  small   cell-bodies   of 
spherical  or  oval  form,  with  a  double  cell -membrane,  the  intine  and 


Fro.  154. — Pollen-grain  of  Epi-    ? 
lobium  angustifolium. 


1  Among  others  MOHL,  CHATIN,  SCHINZ,  PRANTL,  and  SCHBODT  made  special 
studies  of  this  subject. 


REPRODUCTION. 


227 


extine.  The  extine  is  firm  and  cuticularized ;  the  inline  is  soft, 
and  consists  of  cellulose.  The  latter  enters  into  the  formation 
of  the  pollen-tube.  The  points  at  which  the  pollen-tube  forma- 
tion is  to  begin  are  predetermined.  The  extine  (Fig.  154,  e)  is 
supplied  with  one  (monocotyledons),  several,  or  many  (dicotyledons) 
open  or  thin  areas  (0,  a).  In  some  cases  there  is  a  lid-like  cover 
to  these  openings,  which  is  removed  when  the  pollen-tube  begins  to 
develop.  The  intine  (i)  is  usually  thickened  at  these  thin  areas  (see 
Fig.  154).  The  protuberances  and  spines  which  sometimes  occur  on 
the  extine  may  serve  to  attach  the  pollen  to  insects  as  well  as  to  the 
stigma.  The  pollen-grains  result  from  the  quadrature  of  the  pollen 
mother-cells,  which  are  known  as  tetrads  in  the  first  stage.  Fig. 
155  represents  an  early  stage  of  the  pollen-forming  anther-case. 
The  cells  immediately  sur- 
rounding the  pollen  mother- 
<?ells,  (ep)  as  well  as  a  layer 
external  to  these,  are  subse- 
quently dissolved.  The  cells 
(ep)  are  known  as  tapetal 
cells.  Between  the  stage 
represented  in  the  figure 
and  the  mature  stage  the 
young  pollen- cells  are  found 
floating  in  the  granular  liquid 
which  fills  the  entire  anther- 
case.  (Studied  more  in  par- 
ticular by  NAG-ELI,  HOF- 
MEISTER,  and  WARMING). 
The  ripe  pollen-grains  usu- 
ally form  a  powdery  mass.  Orchids  offer  a  peculiar  exception, 
the  ripe  pollen-grains  of  the  entire  anther  remain  united  in  a  single 
mass,  forming  the  pollinium.  The  teleology  of  the  fertilization  of 
orchids  has  been  made  a  special  study  by  DARWIN. 


FIG. 


155. — Cross-section   through   a,   young 
anther-case  of  Funkia  cordata. 

sm,  Pollen  mother-cells ;  ep,  tapetal  layer ;  w,  epi- 
dermis.   (After  Sachs.) 


C.   THE  GYNCECIUM.     THE  OVULE  WITH  THE  EMBRYO-SAO 

BEFORE    AND    AFTER    FERTILIZATION. 

The  gynoecium  (pistil,  according  to  the  older  terminology)  bears 
the  ovules  (seed- buds)  in  the  lower  hollow  portion,  the  ovary.     The 


228 


COMPENDIUM  OF  GENERAL  BOTANY. 


ovules  are,  as  a  rule,  situated  along  the  margins  (placentce)  of  the 
carpellary  leaves  or  leaf.  The  number  of  carpellary  leaves  produces 
either  a  monomerous  or  &  polymerous  gynoecium.  The  polymerous. 
gynoecium  may  either  develop  into  a  single  ovary,  when  it  is  known 
as  a  syncarpous  gynoecium ;  or  each  individual  carpel  may  develop 
a  pistil,  the  polycarpous  or  apocarpous  gynoecium  (Ranunculaeece). 
Fig.  156  represents  a  cross-section  of  the  polymerous  syncarpous 


FIG.  1 56.  —  Cross- 
section  through 
the  ovary  of 
Paris  quadrifo- 
lia. 

(After  Krass  and  Lan- 
dois.) 


FIG.  157.— Ovary  of  Atropa 
Belladonna. 

A.  Longitudinal  section  ;  B,  cross- 
section.  (After  Krass  and  Lan- 
dois.) 


FIG.  158.— Central 
placenta  of  Pri- 
mula qfficinalis, 
with  the  ovules 
removed. 

(After   Berthold  and 
Landois.) 


gynoecium  of  Paris  quadrifolia  /  it  is  usually  known  as  a  "  four- 
chambered  ovary."  Fig.  157  shows  the  polymerous  syncarpous. 
(two-chambered)  gynoecium  of  Atropa  Belladonna. 

The  manner  in  which  the  carpellary  leaf-margins  are  united 
sometimes  brings  the  margins  nearly  to  the  middle  of  the  cavity  of 
the  ovary.  This  produces  what  is  known  as  axillary  placentation- 
(Figs.  156  and  157),  which  is  very  common.  More  rarely  the 
margins  project  little  or  not  at  all  into  the  cavity  of  the  ovary, 
when  it  is  known  as  parietl  placentation  (  Violacece).  There  are 
also  intermediate  forms  of  placentation  which  produce  the  incom- 
pletely many-chambered  ovaries  (Papaver).  The  so-called  central 
placentation  (for  example,  of  the  Primulacece;  see  Fig.  158)  is  not 
well  understood  from  a  morphological  standpoint.  It  seems  as 
though  the  floral  axis  (torus)  produced  the  ovules.  It  is,  however, 
possible  that  a  caulome  may  develop  ovaries.1 

The  Position  and  Form  of  Ovaries. — An  ovule  is  said  to 
be  atropous  (orthotropous)  or  straight  when  it  forms  a  direct  con- 
tinuation with  its  stalklet  or  funiculus.  The  ovule  is  said  to  be 
anatropous  when  the  funiculus  extends  along  and  is  adherent  to  the 


1  For  fear  that  this  statement  may  be  misleading  I  will  state  that  a  caulonie, 
as  sucJi,  will  never  produce  ovaries. — TRANS. 


REPRODUCTION.  229 

side  of  the  ovule.  The  ovule  is  campylotropous  or  curved  when  its 
own  body  is  more  or  less  curved.  An  anatropous  ovule  is  shown  in 
the  diagrarnatic  figure  of  the  angiospermous  flower  (Fig.  132);  the 
two  other  forms  are  represented  in  the  accompanying  figure  159, 
(1  and  2).  In  the  ovule,  exclusive  of  funiculus,  we  distinguish  the 


* —  l    s  s  /^ 

2 
FlG.  159.      (After  Berthold  and  Landois.) 


body  of  the  ovule  (b)  with  the  embryo-sac  (<?)  and  one  or  two 
integuments;  the  latter  (d,  f)  form  the  micropylar  opening  (e). 
The  hilum  is  the  point  where  the  funiculus  (a)  is  attached  to  the 
placenta ;  the  chalaza  (h)  is  the  zone  at  the  base  of  the  ovule  from 
which  the  tegumentary  layers  take  their  origin ;  the  raphe  (seam) 
is  the  line  of  union  between  the  funiculus  and  ovule  in  anatropous 
ovules.  In  semianatropous  (amphitropous)  ovules  the  rnicropyle  and 
chalaza  are  about  equidistant  from  the  hilum  (see  Fig.  159,  3). 
The  anatropic  and  campy lotropic  ovules  may  further  be  apotropous, 
epitropous,  or  pleurotropous,  according  to  whether  the  ovule  is 
turned  toward  the  base  (apotropous),  the  apex  (epitropous),  or  the 
side  (pleurotropous)  of  the  ovary.  Such  variations  in  position  are 
intimately  associated  with  the  function  of  the  pollen -tube. 

The  Ertibryo-sac. — Immediately  before  fertilization  the  embryo- 
sac  of  angiosperms  (monocotyledons  and  dicotyledons)  contains,  as 
a  rule,  three  cells  near  the  micropyle  and  frequently  three  cells  at 
the  opposite  end.  The  latter  have  long  been  known  as  antipodal 
cells,  but  no  particular  function  had  been  ascribed  to  them.  Ac- 
cording to  more  recent  investigations,  they  very  probably  assist  in 
the  processes  of  nutrition.  STBASBURGER'  s  investigations  gave  us  the 
most  important  results  in  regard  to  the  nuclear  divisions  and  fusions 
which  result  in  the  formation  of  the  six  cells  mentioned  and  the 
secondary  nucleus  of  the  embryo-sac  (see  Fig.  132).  One  of  the 
three  cells  near  the  micropyle  takes  up  the  role  of  the  egg-cell. 
The  other  two,  which  are  known  as  the  synergidce,  are  supposed 
to  assist  in  the  process  of  fertilization.  From  the  observations 


230 


COMPENDIUM  OF  GENERAL  BOTANY. 


made  upon  cryptogams  it  is  assumed  that  among  phanerogams 
the  nuclear  substance  (nuclein)  of  the  pollen-tube  enters  the  embryo- 
sac  and  unites  with  the  contents  of  the  egg-cell.  As  a  result  the 
egg-cell  begins  to  develop  into  the  embryo.  The  literature  on 
embryology  is  already  very  extensive.  Special  embryology  has 
succeeded  in  explaining  many  of  the  observed  phenomena  and 
structures.  The  presence  or  absence  of  the  suspensor,  the  behavior 
of  the  antipodes,  the  formation  of  nutritive  substances  in  the  em- 
bryo-sac (endosperm)  as  well  as  on  the  outside  (perisperm),  have 
already  been  explained,  in  part  very  clearly  and  in  part  only  hy- 
pothetically.  They  evidently  serve  important  functions  in  the 
processes  of  growth  in  the  embryo  as  well  as  in  the  young  seedling. 
For  example,  the  suspensor,  which  is  a  simple  cell-thread,  assists 
in  placing  the  embryo  in  that  position  within  the  embryo-sac  at 
which  the  supply  of  nutrition  is  most  favorable.  According  to 
TREUB'S  investigations,  the  suspensor  of  Herminium  Monorchis 
has  the  power  of  forming  protuberances  along  the  placentae.  HOF- 
MEISTER  considered  the  endosperm  as  an  enormously  developed 
suspensor.  ' 

In  regard  to  the  development  of  the  embryo  of  Capsella  (Fig. 
160),  it  should  be  stated  that  among  dicotyledons  the  embryo  nor- 

mally forms  a  depression  at  the 
stem-apex  between  the  two  coty- 
ledons (<?),  while  among  the 
monocotyledons  (Alisma)  the 
elongated  body  of  the  embryo 
is  a  lateral  development  of  the 
stem-  apex  instead  of  a  terminal, 
as  in  the  foregoing.  Other  vari- 
ations also  appear  among  mono- 
cotyledons :  the  originally  ter- 
minal apex  may  later  be  crowded 

FiG.m-Successive  stages  in  the  de-  to  One  side  ^  the  Cot7ledo11- 

velopment  of  a  dicotyledonous  plant,  Among  dicotyledons  there  are 

Capsella  bursa  pastoris.  (Diagramatic.)  ,  .  M  .  ,.  ,,  ~ 

The  dotted  line  in  I  represents  the  wall  of  the  ^SO     deviations     from     the     Cap- 

sella-type  of  embryonal  develop- 


stem,  c  cotyledons. 


ment. 


The   suspensor   is   finally  removed   and   replaced    by    the  de- 


See  also  L.  GUIGNARD,  Ann.  d.  sc.  nat.,  Ser.  VI,  T.  XII,  1881. 


REPRODUCTION.  231 

veloping   root.     HANSTEIN   (following  upon  the  investigations  of 
HOFMEISTER)  made  a  special  study  of  embryonal  development. 

The  effects  of  fertilization  are  not  limited  to  the  gynoecium, 
but  are  manifest  in  the  entire  flower.  Death  and  loss  of  organs 
which  have  served  their  function  go  hand  in  hand  with  new 
processes  of  growth  which  now  serve  new  purposes.  The  petals, 
at  times  also  the  sepals,  fall  off;  the  stamens  wither  away.  Fre- 
quently the  floral  axis  (receptacle,  torus)  takes  part  in  the  fruit- 
formation,  especially  in  epigynous  flowers.  Some  of  the  physiologic- 
al adaptations  are  as  follows:  structural  arrangements  to  enable 
the  seed  and  fruit  to  withstand  the  period  of  vest,  to  distribute  them 
by  wind  and  insects,  and  to  insure  a  favorable  course  during  ger- 
mination. Some  of  these  adaptations  will  again  be  referred  to  in 
the  following  chapters. 

IY.  THE  MORPHOLOGY  AND  PHYSIOLOGY  OF  THE 
SEED   AND   FRUIT   OF   PHANEROGAMS. 

A  fruit  in  the  strict  botanical  sense  is  the  transformed  gynoe- 
cium after  fertilization. 

From  a  single  ovary  results  a  simple  fruit ;  from  several  sepa- 
rate ovaries  of  a  flower  is  formed  the  aggregate  fruit.  From  one 
flower  we  have  a  single  fruit ;  from  an  inflorescence  we  get  the 
multiple  or  collective  fruit  (Ananas,  multiple  fruit ;  cherry,  simple 
and  single  fruit;  Ranunculus,  aggregate  fruit). 

Other  parts  of  the  flower  besides  the  gynoecium  may  take  part 
in  the  formation  of  the  fruit  and  form  false  fruits  in  distinction  to 
the  true  fruits  defined  above.  Example :  the  receptacle  of  the 
strawberry  becomes  fleshy  and  apparently  represents  the  main 
axis  of  the  false  fruit ;  it  is  also  an  aggregate  fruit,  since  many  sepa- 
rate ovaries  (akenes)  are  situated  upon  the  pulpy  receptacle.  The 
apple  is  also  a  false  fruit,  since  the  hollow  floral  axis  (cupuld)  takes 
part  in  its  formation.  The  pappus-like  developments  on  the  fruits 
of  Composite  are  modifications  of  the  calyx. 

Single  fruits  may  be  divided  into  five  kinds:  1,  capsule ;  2, 
carpels;  3,  achenium  (akene) ;  4,  drupe /  5,  berry.  (See  figures 
on  p.  234.) 

1.  The  capsules  open  at  maturity  according  to  a  fixed  method. 
They  may  be  subdivided  as  follows. 


COMPENDIUM  OF  GENERAL  BOTANY. 

(a)  The  legume  or  true  pod  is  a  single-chambered  fruit  formed 
from  one  carpel ;   seeds  are  placed  along  the  ventral  suture ;   dehis- 
cence  along  the  dorsal  and  ventral  suture  from  above  downward 
(Leguminosoe). 

(b)  T\\Q  follicle  opens  along  the  ventral  suture  only  (Pceonia). 

(c)  The  silique,  two- chambered ;   dehisces  along   both  sutures 
from    below   upward;    the  placentae,    as    the    partition,    remain 
behind  while  the  valves  fall  away  (Cruciferm). 

(d)  True  capsules,  usually  dehisce  from  the  apex  downward, 
or  they  may  discharge  the  ovules  through  chinks  or  pores,  as  -in 
Papaver  •   they  may  open  at  the  teeth-like  projections  near  the 
apex,  as  in  Primula;  by  valves  opening  lengthwise,  as  in  Iris  and 
8yringa\   or  transversely,  as  in  Colchicum  autumnale ;  or  by  the 
dissolving   of  the   partition,  as   in  Datura.     We   may  therefore 
recognize  loculicidal,  septicidal,  and  septifragal  dehiscence. 

2.  Carpels  (splitting  fruits)  are  again  divided  into : 

(a)  Cremocarp,  consisting  of  a  pair  of  akene-like  ovaries  com- 
pletely united  in  the  blossom,  but  splitting  apart  when  mature 
(  Umbelliferce). 

(b)  Loment  resembles  a  legume,  but  splits  up  crosswise  at  dis- 
tinct joints  or  transverse  septa  (Desmodium). 

The   achenium,  drupe   (stone-fruit),  and  berry   do   not  open 
according  to  such  systematic  methods. 

3.  The  achenium  is   usually  small  with  a  dry  woody  coat. 
This  fruit  may  again  be  divided  into :    (a)  achenium  proper,  (b) 
caryopsis.     .In  both  the  seed  is  closely  united  witli  the  seed-cover- 
ing or  pericarp.      The  achenium  arises  from  inferior  ovaries  (Com- 
positce),  the  caryopsis  from  superior  ovaries,      (c)  Samara  or  key- 
fruit,  which  is   an   akene   furnished  with    wing-like   appendages 

(elm,  ash,  maple),  (d)  Nut;  this  as  well  as  the  key-fruit  has  free 
seeds  lying  within  the  seed-covering.  The  covering  of  the  nut 
consists  of  typical  sclerenchyma  cells  (hazelnut,  chestnut,  acorn, 
etc.). 

4.  Drupe  (stone -berry).     The  inner  layer  of  the  fruit-cover- 
ing (endocarp)  is  very  hard ;  the  outer  layer  (including  mesocarp 
and  epicarp)  is  succulent  and  much  enlarged,  as  in  our  stone-fruits, 
the  cherry,  plum,  etc.  ;  or  it  may  be  dry  and  fibrous,  as  in  the 
cocoanut ;   or  almost  leathery,  as  in  the  walnut  and  almond.     (The 
entire   fruit- covering   is   usually   known    as   the    pericarp.)     The 


REPROD  UCTION.  233 

apple-fruit  (pome)  may  be  considered  as  a  stone-berry  with  a  thin 
pergament-like  endocarp  (RADLKOFER,  WARMING). 

5.  Berries.  The  entire  pericarp  is  soft  and  fleshy,  or  leathery 
at  the  outer  part  (grape,  tomato,  orange). 

(The  foregoing  description  of  fruit  -  forms  is  according  to 
THOME.) 

There  are  many  structural  arrangements  to  facilitate  the  distri- 
bution of  seeds  and  fruits.  Although  the  physiological  factors 
were  not  considered  in  the  description  of  fruit-forms,  we  must  not 
for  a  moment  forget  that  such  factors  nevertheless  exist,  some 
of  which  have  been  carefully  worked  out,  while  others  require 
further  elucidation.  In  1873  HILDEBRAND  published  his  com- 
munication on  the  Distribution  of  Seeds  by  Plants,  to  which 
I  refer  the  student,  and  from  which  the  following  statements  are 
taken. 

The  following  peculiarities  of  seeds  and  fruits  facilitate  their 
distribution  by  air-currents. 

1 .  Reduced  size  of  seeds  (including  the  spores  of  cryptogams) ; 
lightness  of  seeds  (orchids). 

2.  Flat  form  of  seeds  (Lilium,  Tulipa) ;  wing-like  appendages 
(conifers,  many  crucifers). 

3.  Wing-like  appendages  of  fruits  ( Ulmus,  Fraxinus,  Betula, 
Acer,  Rheum,  Isatis) ;  the  winged  appendages  may  also  be  formed 
by  modified  bracts  (linden,  hawthorn),  or  by  the  perianth  (Salsola). 

4.  Hair-like  appendages  to  seeds  (Epilobium,  Salix,    Gossy- 
pium). 

5.  Hair-like  and  feather-like  appendages  to  fruits  (Anemone, 
Composite^). 

(The  following  figures  will  assist  in  explaining  fruit-forms  as 
well  as  the  appendages  just  referred  to.) 

We  must  also  mention  the  arillus  or  seed-mantle  with  which 
many  seeds  are  equipped.  It  may  develop  from  the  funiculus,  the 
hilum,  or  the  micropyle.  In  the  seeds  of  Evonymus  europcea  it 
is  of  a  yellowish-red  color ;  in  seeds  of  Taxus  it  is  well  developed 
and  red  in  color.  Such  highly  colored  formations  attract  animals, 
especially  birds,  which  feed  upon  the  seed.  Other  structural 
arrangements  for  the  successful  distribution  of  seeds  are  the  thick 
and  hard  seed-coverings  (testa),  which  resist  the  digestive  action  of 
the  juices  of  the  stomach  and  intestines  of  animals.  Animals, 


234 


COMPENDIUM  OF  GENERAL  BOTANY. 


FIG.  161.— Pod. 

(After  Berthold  and 
Landois.) 


FIG.  162.— Pod  of  Bras- 

sica  Napus. 
(After  Krass  and  Landois.) 


FIG.    163.— Seed-capsule    (open)  of 
Epilobium  augustifolium.    Tufted 
(After  Berthold  and  Landois.) 


FiG.165.— Wing- 
ed fruit  of  the 
elm. 

(After  Berthold  and 
Landois.) 


FIG.  164.— Achenium  (a) 
with  parachute-like  ar- 
rangement of  the  "  pap- 
pus (J)."  Taraxicum 
officinale. 

(After  Berthold  and  Landois.) 


FIG.  166. — Akeues  of  Anemone  pulsa- 

tilla  with  the  long  hair-like  styles. 

(After  Berthold  and  Landois.) 


FIG.  167.— Pods  of  Ornitho- 

pus. 
(After  Berthold  and  Landois.) 


FIG.  168.—  Salix  Cavrea. 

a  and  6,  Fruit;  c.  seed.    (After  Krass  and  Landofs.V 


REPRODUCTION.  235 

especially  birds,  may  carry  these  seeds  great  distances  on  land  or 
across  the  water. 

In  some  cases  the  arillus  has  an  entirely  different  function. 
Among  Leguminosce  it  forms  a  scission  tissue  between  the  placenta 
and  the  seed,  causing  delicate  tissues  to  rupture.  In  Nymphcea 
the  arillus  serves  to  keep  the  seed  afloat.  The  seed  floats  upon 
the  surface  of  the  water  for  about  forty-eight  hours,  so  long  as 
there  is  air  in  the  cavity  of  the  arillus ;  as  soon  as  water  displaces 
the  air  the  seed  takes  a  position  with  its  apex  upward  and  falls  out 
of  the  sac  to  the  bottom  of  the  water,  where  it  begins  to  germinate. 
In  various  families  (Berber  idacem,  Turneracece)  the  arillus  serves 
the  same  function  as  the  winged  appendages  of  seeds.1 

Leaving  out  of  consideration  the  arillus,  which  is  not  always 
present,  we  have  yet  to  discuss  the  seed-coat.'  Sometimes  we  may 
distinguish  two  layers,  an  inner  (tegmen)  and  an  outer  (testa), 
which,  however  do  not  always  originate  as  two  separate  coats 
(RADLKOFER).  The  above-mentioned  winged  and  hair-like  ap- 
pendages are  products  of  the  seed-coats.  In  some  seeds  there  are 
still  other  hair-like  appendages  which  serve  to  attach  the  seed  to 
the  soil  during  germination. 3  This  is  also  the  case  in  some  fruits. 
The  mucilaginous  cell- walls  of  the  outer  seed-coat  serve  a  similar 
purpose,  as  in  Linum  usisatissimum,  OrucifercB,  Labiatce.  The 
mucilage  also  retards  the  evaporation  of  moisture  from  the  seed 
(KLEBS). 

The  endosperm,  which  we  have  already  learned  to  know,  needs 
to  be  considered  more  from  a  physiological  standpoint,  especially  in 
connection  with  the  discussion  of  seed-  and  fruit-coats.  Commu- 
nications and  citations  of  literature  in  regard  to  this  subject  are 
found  with  MARLOTH.*  In  1890  "W.  HIRSCH  published  a  commu- 


1  PLANCHON,  BAILLON,    HILDEBRAND,  BACHMANN,   PFEIFFER,  and  others, 
from  whom  we  have  taken  the  foregoing  statements,  made  special  studies  of  thi& 
subject. 

2  See  PPEFFER'S  Untersuchungen  a.  d.  Botanischen  Institut  zu  Tubingen. 
FRANK  gives  numerous  citations  to  the  literature  of  this  subject  in  his  Lehrbuch 
der  Botanik,  p.  159  (1892).     See  also  R.  LOOSE,  Die  Bedeutung  der  Frucht  und 
Sameuschale,  etc.,  Berlin,  1891. 

3  GRUTTER,  W.,  liber  den  Bau  und  die  Entwickelung  der  Samenschalen  eiui- 
ger  Lythrarieen,  Bot.  Zeitung,  1893.— TRANS. 

4Uber  mechanische  Schutzmittel  der  Samen,  etc.,  Botanische  Jahrbucher  IV> 
1883. 


236  COMPENDIUM   OF  GENERAL  BOTANY. 

nication  on  The  Adaptive  Arrangements  of  the  Storage -tissue  of 
Seeds. 

The   chief   function   of   the    seed- coat   is   purely    mechanical, 
forming  a  protection  against  radial  pressure.      Seeds  must  be  pro- 
tected against  injury  during  their  transport  to  the 
places  of  germination ;  they  must  also  be  protected 
during  their  rest  in  the  soil  against  the  attacks  of  ani- 
mals.     Protection    against   evaporation   usually  goes 
hand  in  hand  with  mechanical  protection.     The  fact 
that  the  formation  of  thick- walled  mechanically  active 
cells  may  take  place  not  only  in  the  seed-  or  fruit- 
coats,  but  also  in   the  seed-albumen  (endosperm),  is 
highly  interesting.      Much  requires  further  investiga- 
tion, but  we   are  enabled  at  present  to  arrange  the 
"  following  "  biological "  groups    of  plants:   1.    The 
section   of    a  seed-coat  consists  of  thin-walled  cells  and  encloses  the 
endosperm  of  thick- walled  albumen   of  the    seedling :    Colchicum, 
vuiya™atUm  ViSGum,   Plantago,  Arum,   Rubiacece.     2.    Thick- 
(After  Haber-    walled  cells  of  the   seed-coat  and  thin-walled  endo- 
sperm :  Syringa,  Saxifragacece,  Helleborus,  Papaver^ 
Glaux,    Ilippophce,    Giaminecv.     (After    MARLOTH.)      (Compare 
Tigs.  91  and  169.) 

In  still  other  cases  both  the  seed-coat  and  the  endosperm  take 
part  in  forming  the  mechanical  tissue.  PFITZER  '  made  some  very 
interesting  observations  in  regard  to  the  adaptations  for  the  germi- 
nation of  seeds  with  hard  fruit-coats,  as  those  of  the  Palmce. 
Based  upon  his  communication  I  will  state  that  among  the  Boras- 
^since  the  points  for  the  escape  of  the  seedling  are  preformed.  The 
thinnest  part  of  the  fruit-coat  is  immediately  in  front  of  the 
embryo.  In  Cocos  there  is  a  valve  a.t  the  point  of  germination 
which  is  readily  removed.  This  valve  or  opening  corresponds  in 
position  to  the  style.  Pfitzer  also  found  special  arrangements  for 
holding  the  endosperm  of  the  ripe  fruit  so  that  the  seedling  must 
retain  its  proper  position  in  regard  to  the  germinal  opening,  as,  for 
example,  conical  projections  from  the  seed-coat  into  the  endosperm- 
substance. 

On  pp.  142,  143  we  have  explained  more  or  less  clearly  that 


1  Ber.  d.  Deutscb.  Bot.  Ges.,  1885. 


REPRODUCTION.  237 

the  seedlings  of  Cruciferce  and  Papilionacece,  which  are  without 
endosperm,  present  physiologically  similar  structures  in  the  much- 
thickened  cotyledons  (rich  in  oil). 

We  will  not  enter  into  a  discussion  of  the  arrangements  for  the 
ejection  of  seeds  from  the  ovaries  and  fruits.  We  will  only  men- 
tion a  peculiarity  of  the  seeds  of  JErodium,  namely,  under  favorable 
circumstances  they  are  forced  into  the  ground  by  the  movements 
of  the  hygroscopic  awn.  In  Arachis  hypogcea  (peanut)  the  basis  of 
the  ovary  grows  downward,  carrying  the  young  ovary  into  the  soil, 
where  it  matures.  Some  of  the  mechanical  movements  will  be 
more  fully  explained  in  the  chapter  on  the  phenomena  of  move- 
ments. 

GERMINATION. 

Germination  takes  place  after  the  period  of  rest,  provided  there 
is  sufficient  moisture,  a  temperature  varying,  as  a  rule,  from  6°  C.  ta 
45°  C.  (SACHS),  and  air  (O).  Light  is  therefore  not  necessary. 
The  appropriation  of  oxygen  will  be  discussed  later. 

The  duration  of  the  mobility  of  seeds  is  limited,  but  differs 
greatly  in  different  plants.  Some  seeds  must  be  placed  in  the  soil 
at  once  (coffee),  many  others  can  germinate  at  once  or  later ;  some 
remain  viable  only  during  one  vegetative  pause  (winter) ;  others 
several  or  many  years.  The  reports  that  seeds  one  thousand  or  twa 
thousand  years  old  were  still  capable  of  germination,  are  questionable. 
Many  seeds  can  not  germinate  immediately  after  their  separation 
from  the  mother-plant.  According  to  SACHS,  potatoes  and  onions 
cannot  send  out  shoots  during  November  or  December  of  the  same 
season  in  which  they  were  formed. 

The  subject  of  the  ; '  rest- period  "  of  seeds  as  well  as  "  rest  " 
in  general  (tubers,  bulbs,  buds  rest  also)  is  more  difficult  of  explana- 
tion than  one  would  suppose.  The  following  statement  is  accord- 
ing to  the  authority  of  SACHS  ' :  We  may  assume  that  seeds,  bulbs, 
etc. ,  which  are  capable  of  germinating  at  once  receive  the  neces- 
sary amount  of  ferment  during  their  formation  while  still  con- 
nected with  the  mother -plant ;  in  other  cases  a  longer  period  (and 
perhaps  lower  temperature)  is  required  to  form  the  necessary  fer- 
ment. These  ferments  (as,  for  example,  the  starch- dissolving  dias- 


Vorlesungen,  p.  425. 


238  COMPENDIUM  OF  GENERAL  BOTANY. 

tase)  must  be  present  in  order  that  the  reserve  materials  may  be 
dissolved,  since  they  cannot  be  utilized  in  the  processes  of  nutrition 
while  in  the  solid  state. 

In  regard  to  the  "  annual  vegetative  period,"  we  soon  recog- 
nize that  this  phenomenon  needs  further  elucidation  (PFEFFER).' 
According  to  my  opinion,  the  investigation  of  the  properties  and 
peculiarities  of  organisms  reveal  relations  and  adaptations  which 
we  can  recognize  as  such  without  being  able  to  explain  them.  Let 
us  consider  a  few  examples.  1.  We  can  see  that  the  annual  peri- 
odicity is  not  peculiar  to  all  plants ;  the  regularly  recurring  period 
of  rest  seems  to  be  a  "  facultative  ' '  property  of  many  plants 
which  manifests  itself  when  desirable.  2.  We  can  also  see  that 
definite  plant-forms  are  adapted  to  definite  external  relations. 

Ad  1.  Many  tropical  plants  while  in  their  natural  home 
develop  leaves  and  flowers  during  the  entire  year.  If,  however, 
an  annual  dry  period  sets  in,  as  is  very  common  in  tropical  regions, 
we  notice  that  such  plants  undergo  a  periodic  rest,  corresponding 
to  the  dry  seasons. 

Ad  2.  Climatic  adaptability  will  have  reached  its  limit  when 
palms  can  survive  in  our  climate  without  artificial  protection.  Our 
native  oak  and  beech  can  exist  in  Madeira,  but  will  shed  their  leaves 
in  spite  of  the  moist,  mild  climate.  The  cherry  is  evergreen  in 
Ceylon,  but  does  not  develop  fruit  (DE  CANDOLLE).  According  to 
HUMBOLDT,  the  grape  of  Venezuela  bears  leaves  and  fruit  during 
the  entire  year.  HARNIER  noticed  the  same  thing  in  the  grapes 
of  central  Africa  (Khartoum). 

Y.   THE  GENERAL  PHYSIOLOGY  OF  REPRODUCTION. 

In  this  chapter  the  statements  are  based  essentially  upon  the 
investigations  of  NAGELI  and  in  part  upon  those  of  SACHS,  unless 
other  citations  are  given. 

A.   AGENTS  IN  FERTILIZATION.     CROSS-POLLINATION.     SELF- 
POLLINATION. 

PFEFFER'S  recent  investigations  have  revealed  the  cause  which 
induces  the  free-swimming  spermatozoids  of  cryptogams  to  move 


Pflanzenphysiologie,  II,  106. 


REPRODUCTION.  239 

toward  the  archegonia.  It  is  a  chemical  agent.  Among  ferns  it 
is  malic  acid,  among  leafy  mosses  it  is  cane-sugar,  which  acts  as  the 
peculiar  stimulus  that  attracts  the  spermatozoids  to  the  opening 
of  the  archegonium.  Among  phanerogams  the  pollen-grains  are 
transferred  to  the  stigma  (or  micropyle)  by  means  of  insects  or  the 
wind.  Plants  dependent  upon  the  wind  for  pollination  are  said  to 
be  anemophilous  •  those  dependent  upon  insects  are  entomophi- 
lous.  In  some  plants  pollination  is  dependent  upon  water- cur- 
rents ;  they  are  said  to  be  hydrophilous. 

The  great  majority  of  phanerogamic  flowers  are  structurally 
adapted  to  be  fertilized  by  other  flowers  of  the  same  species ;  they 
are  open  at  the  appropriate  time  :  chasmogamous  flowers.  There 
is  also  a  small  group  of  plants  dependent  upon  self-fertilization  and 
whose  flowers  therefore  remain  closed  :  deistogamous  flowers.  Ex- 
ample :  Ranunculus  aquatilis. 

A  study  of  these  relations  gives  us  an  insight  into  a  large  num- 
ber of  adaptive  arrangements.  Some  of  the  subsequent  statements 
are  repetitions,  but  will  not  be  amiss,  because  of  the  importance  of 
the  subject.  The  anemophilous  plants  have  inconspicuous  flowers 
of  dull  colors  and  very  numerous  pollen-grains ;  they  sometimes 
bloom  before  the  appearance  of  the  leaves.  Examples :  Gymno- 
spermce  and  Graminece.  In  the  former  (Pinus)  the  pollen -grain 
may  have  winged  appendages.  The  entomophilous  flowers  require 
and  possess  large  showy  flowers,  with  odor  and  nectaries  for  the 
purpose  of  attracting  insects. 

From  the  frequent  occurrence  of  hermaphroditic  flowers  among 
phanerogams  it  must  not  be  concluded  that  self-pollination  is  the 
rule.  The  majority  of  hermaphroditic  flowers  as  well  as  flowers 
in  general  are  specially  adapted  for  the  process  of  cross-pollination. 
Of  such  adaptations  the  three  following  may  be  mentioned  without 
considering  the  mechanical  structures  thereby  involved.  1  and  3 
refer  to  hermaphroditic  flowers. 

1.  Dichogamy.  The  androecium  and  gynoecium  of  the  same 
flower  do  not  mature  at  the  same  time.  If  the  anthers  mature  first, 
it  is  known  as protandry  (Compositce) ;  if  the  pistil  matures  first, 
it  is  known  as  protogyny  (as  in  Plantago  media).  Though  cross- 
pollination  is  the  rule,  hermaphroditism  is  not  an  unsuitable  ar- 
rangement; by  it  is  represented  the  largest  possible  number  of 
flowers  of  both  sexes  writh  the  least  expenditure  of  substance. 


240  COMPENDIUM  OF  GENERAL  BOTANY. 

Furthermore,  it  is  clear  that  since  the  visit  of  insects  depends  upon 
the  existing  plan  of  organization  it  also  guarantees  the  greatest 
success. 

2.  Dicliny.     It  is  either  monoecious ,  that  is,  male  and  female 
flowers   occur   upon   the   same   plant   (example :    Zea   Mays),   or 
diwciouS)  if  the  sexes  occur  upon  different  plants  (examples :  Salix, 
Conifer  ce). 

3.  Heterostyly.      In   plants   of  the  same   species  (examples : 
jPrimulacece,  Lythrum  Salicaria)  there  may  be  two  or  three  sets 
of  stamens  differing  in  length  (dimorphism ,  trimorphism) ;   corre- 
sponding to  these  stamens,  the  pistils  are  also  of  different  lengths. 
The  following  is  the  principle  underlying  this  arrangement.     That 
part  of  the  body  of  the  insect  which  comes  in  contact  with  the 
stamens  of  the  length  a  of  one  flower  also  comes  in  contact  with 
the   stigma  of   the   same  length  of   another   flower.     The  above 
method  of  pollination  produces  the  best  results,  as  has  been  verified 
by  control  experiments.     It  has  also  been  observed  that  in  flowers 
with  elements  of  unequal  length  the  female  flowers  are  more  or 
less  sterile.     In-and-in  breeding  (Inzucht)  is  the  term  applied  to 
that  form  of  reproduction  which  occurs  in  the  same  plant-forms,  in 
distinction  to   hybridization    (crossing).     We    also  know   that  the 
most  common  form  of  crossing  is  by  two  different  individuals  of 
the  same  species  (cross-fertilization  in  the   narrower  sense),    the 
special  organization  of  which  we  have  just  learned  to  know.     There 
are,  however,  certain  plants  with  flowers  especially  adapted  for  self- 
pollination  (HERMANN  MULLER  made  a  special  study  of  this  adapta- 
tion).    Many  land-plants  open  their  flowers  only  partially  or  not  at 
all  on  rainy  days  (  Veronica  hedercefolia,  Drosera  rotundifolia) ; 
the   submerged  flowers  of   water-plants  also  remain  closed,    and 
pollination  takes   place  in  the  small  air-space   between  the  floral 
coverings.1    Example:  Ranunculus  aquatilis.    Such  cleistogainous 
flowers  develop  much  less  pollen  than  the  chasmogamous  flowers, 
which  are  dependent  upon  wind  and  insects  for  pollination.     The 
cleistogainous  flower  of  Viola  nana  forms  about  100  pollen-grains, 
while  an  entomophilous  flower  of  Leontodon  forms  about  243,600. 


SCHENK,  Biologie  der  Wassergewachse. 


REPRODUCTION.  241 


B.  FERTILE  SEEDS.     HYBRIDIZATION.     APOGAMY. 

In  regard  to  the  production  of  fertile  seeds,  the  following  factors 
are  of  prime  importance. 

I.  Only  one  pollen-tube  is  engaged  in  fertilizing  an  ovule.     If 
pollen-grains  from  different  species  of  plants  fall  upon  the  same 
stigma,  only  that  one  will  be  active  in  fertilization  which  has  the 
greatest  sexual  affinity  (see  II).     According  to  recent  investigations, 
it  is  necessary  that  some  of  the  nuclear  substance  of  the  pollen-tube 
(male  pronudeus)  fuses  with  the  nuclear  substance  of  the  egg- cell 
(female  pronudeus).    The  manner  in  which  the  pollen-tube  readies 
the  egg-cell  has  already  been  described. 

II.  We  must  distinguish  between  systematic  and  sexual  rela- 
tionship;  they  are  not  identical.     The  latter  may  be  ascertained 
by  methods  of  crossing ;  the  former  we  judge  by  the  similar  or  dis- 
similar  characteristics.       Plant-forms   which   are  widely   separate 
systematically  are  often  closely  related  sexually,  that  is,  they  can 
be  crossed;  as,  for    example,   Lychnis  diurna   and  Lychnis  flos 
cuculi  ;  while  Pirus  malus  and  Pirus  communis  (apple  and  pear) 
show  only  slight  sexual  affinity  or  perhaps  not  any.      Species  of 
Dianihus  are  readily  crossed ;  species  of  Silene  with  difficulty  or  not 
at  all;   Rosacem,  Salicacece  with  comparative  ease;   Papilionacece 
with  difficulty ;  etc.     It  is  further  interesting  to  note  that  while 
a  may  be  fertilized  by  5,  b  will  not  be  fertilized  by  a  (non-recipro- 
cal or  imperfectly  reciprocal   hybridization).      Different  varieties 
cross  very  readily  (variety -hybrids),  different  species  less  readily 
(species-hybrids),  different  genera  very  rarely  (genus-hybrids).     The 
following  statement  is  generally  applicable  :  Only  such  plant-forms 
as  show  a  close  systematic  relationship  can  be  successfully  crossed. 
This  does  not  preclude  the  possibility  that  the  fertilization  between 
varieties  may  be  more  effective  than  fertilization  between  two  in- 
dividuals of  the  same  variety. 

III.  Fertility    and    other   conditions   of   hybridization.       The 
sexually  produced  offspring  of  two  plant-individuals  which  do  not 
belong  to  the  same   systematic  unity,  but  to  different  varieties, 
species,  or  genera,  are  called  hybrids  (bastards}.     The  greater  the 
difference  in  the  systematic  affinity  of  the  parents  of  a  hybrid  the 
greater  the  liability  to  sterility.     Widely  separate  species  do  not 


242  COMPENDIUM  OF  GENERAL  BOTANY. 

form  hybrids ;  slightly  related  species  may  form  a  sterile  hybrid. 
(The  hybrid  between  the  apple  and  pear  would  be  sterile.)  Closely 
related  species  will  form  hybrids  with  limited  fertility,  at  least 
they  are  less  fertile  than  the  parental  forms.  Vegetatively  the 
hybrids  are  often  much  stronger  than  the  parental  forms;  they 
' '  luxuriate. ' ' 

IV.  According   to  NAGELI,   the  male  and  female  hereditary 
qualities  are  about  equally  transmitted  in  the  hybrid.     This,  how- 
ever,  does  not  imply  that   the  hybrid  AB  (resulting  from   the 
fertilization  of  A  by  B,  presents  the  same  peculiarities  as  the  hy- 
brid BA.     Nageli  maintains,  however,  that  the  hybrid  can  have 
no  properties  or  peculiarities  not  contained  in  the  ancestral  forms, 
nor  can  there  be  anything  lost  which  is  contained  in  the  ancestral 
forms.     Peculiarities  may  lie  dormant  and  become  entirely  lost,  or 
may  develop  later  (reversion,  atavism).     Such  latent  qualities  do 
not   develop  when  varieties  of  cultivated   plants  are  propagated 
asexually ;  by  this  means  the  race  or  species  may  be  kept  almost 
unchanged  and  it  is  extensively  utilized  by  horticulturists  in  propa- 
gating desirable  fruits  and  flowers.     Propagating  from  the  seeds  of 
such  races  shows   c '  degeneration ; ' '  that  is,  their  latent  qualities 
develop  (NAGELI).     A  hybrid  AB  which  resembles  A  more  nearly 
than  B  will  revert  more  rapidly  to  the  parental  form  A  if  con- 
tinually fertilized  by  A  than  into  the  parental  form  B  by  continu- 
ous fertilization  by  B. 

V.  There  are  also  ' c  derived ' '  hybrids.     They  result  when  one 
hybrid  and  one  of  its  parental  forms,  or  some  other  parental  form 
or  hybrid,  unite  sexually.     There  are  also  cases  in  which  four  or 
more  varieties  or  species  may  be  represented  by  one  hybrid.     MIL- 
LAKDET'S  *  experiments  with  the  grape  have  enabled  us  to  make  great 
practical   use   of  hybridization.     In   North  America  there  are  a 
number  of  wild-growing  species  of  Vitis  which  can  be  crossed. 
Of  our   European  Vitis  vinifera   not  a  single   variety   is   proof 
against  the  attacks  of  the  grape-louse  (Phylloxera].     According  to 
Millardet,  a  hybrid  formed  by  crossing  different  American  species 
with  the  European  species  produces  a  grape  which  will,  to  a  certain 
extent,  resist   the  attacks  of  Phylloxera  and  various  destructive 
fungi. 


See  SACHS'  Vorlesungen,  p.  961. 


REPRODUCTION.  243 

VI.  Finally,  we  will  briefly  mention  the  rare  occurrence  of 
* '  apogamy ' '  and  related  phenomena  (DE  BARY  and  his  pupil  FAR- 
LOW)  .  It  has  been  observed  that  among  some  ferns  a  plant  will 
develop  from  the  prothallium  without  fertilization,  hence  asexually 
(budding).  According  to  A.  BRAUN  (1856),  the  egg-cell  of  Chara 
crinita  may  develop  into  an  embryo  without  being  fertilized.  The 
egg-cell  of  the  euphorbiaceous  genus  -Ccelebogyne  will  also  develop 
by  budding.  Only  the  female  plant  occurs  in  Europe. 

C.   VARIABILITY.     CONSTANCY.     HEREDITY. 

The  properties  of  a  plant  as  a  whole  may  be  separated  into 
those  which  are  constant  and  those  which  are  variable.  Con- 
stancy and  variability  are  clear  conceptions,  but  their  application 
in  regard  to  heredity,  sex,  and  environment  soon  bring  to  light 
great  difficulties. 

Constancy  is  the  result  of  heredity  acting  from  one  generation 
to  another ;  the  influence  of  both  parent-plants  upon  the  daughter- 
plant.  Variability  is  shown  in  slight  differences  between  the 
daughter- plants  among  themselves  and  in  the  differences  between 
daughter-plants  and  parents.  (According  to  Nageli,  heredity  and 
variability  are  almost  inseparable ;  variability  depends  on  heredity.) 

To  us  variability  and  constancy  (hence  also  heredity)  are  prop- 
erties given  to  living  created  beings.  There  is  no  satisfactory 
scientific  definition  for  heredity. 

The  following  statements  are  in  accordance  with  our  present 
knowledge  of  variability.  There  is  a  variability  due  to  external 
causes,  such  as  the  influence  of  the  surrounding  medium,  climatic 
conditions,  etc. ;  and  a  variation  due  to  internal  causes  which  can- 
not be  perceived  externally.  The  latter  causes  are  least  under- 
stood. The  external  causes  can  only  be  interpreted  teleologically ; 
we  are  unable  to  give  them  an  ultimate  causal  explanation.  We 
will  cite  an  example  of  variation  due  to  external  causes.  Poly  go  - 
num  amphibium  usually  grows  near  the  margins  of  ponds,  but  may 
also  occur  on  dry  land.  It  has  been  observed  that  the  anatomical 
structure  of  the  land-form  is  different  from  that  growing  in  water. 
In  the  former  the  intercellular  aerating  system  is  slightly  developed, 
while  the  vascular  system  is  strongly  developed.  In  the  water- 
form  the  reverse  is  true ;  the  air-chambers  are  large,  which  insures 


244  COMPENDIUM  OF  GENERAL  BOTANY. 

a  supply  of  air  and  facilitates  floating ;  the  vessels  are  less  numer- 
ous than  in  the  land-form.  This  shows  that,  there  is  a  suitable 
adaptability  between  the  external  environment  and  the  anatomical 
structure.  Physiology  is,  however,  unable  to  explain  these  causal 
relations.  It  cannot  explain  why  a  locality  deficient  in  water  will 
decrease  the  intercellular  spaces  and  increase  the  vascular  bundles. 
We  can,  however,  understand  somewhat  the  suitableness  of  such 
adaptation.  If  we  recognize  such  knowledge  as  an  explanation  of 
the  cause,  we  make  an  inexact  use  of  the  expression,  since  we  pre- 
suppose something  as  known  which  is  unknown.1  Below  we  will 
have  more  to  say  about  the  variation  of  plant-forms  and  the  effec- 
tiveness of  external  and  internal  causes.  We  will  conclude  this 
chapter  with  a  remark  on  constancy. 

Na'geli2  makes  a  sharp  distinction  between  constancy  in  the 
narrower  sense  (constancy  in  time)  and  permanence  (constancy  in 
space).  What  we  usually  call  "  constancy "  can  generally  only 
have  reference  to  space.  We  compare  individuals  developed  at  the 
same  time  in  different  localities.  Constancy  in  time  (real  con- 
stancy) is  usually  not  tested  by  the  systematist.  This  would  be 
done  by  securing  the  same  species,  or  varieties  from  different 
localities  and  cultivating  them  for  years  under  the  same  environ- 
ment. 

We  will  now  discuss  the  differences  between  the  theory  of 
special  creation  and  the  theory  of  natural  descent. 

D.   SPECIAL  CREATION  AND  THE  SO-CALLED  THEORY  OF 
NATURAL  DESCENT. 

The  doctrine  that  the  first  plant-forms  sprang  from  lifeless 
matter  at  the  command  of  the  Creator,  hence  were  formed  in  a 
supernatural  way,  is  in  no  wise  contradictory  to  the  teachings  of 
natural  history.  We  learn  from  the  book  of  Genesis  (1)  that 
a  series  of  different  plant  -  species  were  created,  (2)  that  the 
"  earth,"  hence  lifeless  matter,  brought  forth  the  plants.3  Chem- 


1  Iii  connection  with  this  statement  it  might  be  well  to  remind  the  student  who 
is  inclined  toward  speculative  reasoning  that  all  knowledge,  no  matter  what  it  may 
be,  is  based  upon  something  which  is  unknown,  and  which  is  therefore  taken  for 
granted. — TRANS. 

2  Mech.-physiolog.  Theorie  der  Abslammungslehre,  1884. 

3  It  is  a  questionable  proceedure  for  a  modern  scientist  to  quote  the  writings 


REPRODUCTION.  245 

istry  teaches,  in  fact,  that  the  plant-bodies  do  not  contain  any  other 
elements  than  those  which  are  found  in  lifeless  matter.  Whether 
dead  substances  are  capable  of  bringing  forth  simple  vegetable 
organisms  at  the  present  time  is  of  no  great  consequence.  Science 
at  present  denies  any  such  origin  of  simple  organisms,  since  all  ex- 
perimentation is  in  support  of  such  a  denial.  This  is  to  be  especially 
emphasized,  because  it  is  generally  believed  that  to  assume  the  aid 
of  a  supernatural  agency  in  forming  living  organisms  from  dead 
matter  is  unscientific.  In  regard  to  higher  plants,  the  agreement 
is  universal  that  there  is  no  origin  de  novo.  This  being  the  case, 
the  question  for  discussion  is,  Where  do  the  higher  vegetable 
organisms  come  from?  Are  they  specially  created,  or  have  they 
descended  in  a  natural  way  from  pre-existing  lower  forms? 

Let  us  test  the  theory  of  natural  descent,  which  teaches  that  all 
plants  have  the  same  phylogenetic  origin  and  firmly  denies  any 
supernatural  creation  either  now  or  in  the  past.  We  will  present 
and  criticise  the  views  of  one  of  its  strongest  advocates,  namely, 
NAGELI. 

According  to  Nageli,  nothing  is  permanently  fixed  or  unchange- 
able— neither  the  variety,  nor  the  species,  nor  the  genus,  family, 
order,  nor  class,  etc.  The  variety  shows  a  certain  constancy,  leav- 
ing out  of  consideration  the  ' '  modifications  due  to  locality ;  "  a 
greater  constancy  is  noticeable  in  the  species;  the  genus  is  still 
more  constant;  and  so  on  up.  We  maintain  that  a  number  of 
forms  or  types,  which  need  not  correspond  with  any  species  of  our 
present  classification,  were  created;  it  is  impossible  to  say  whether 
these  created  and,  to  a  certain  extent,  variable  forms  corresponded 
in  the  one  case  to  a  species,  in  another  to  a  genus,  or  perhaps  to  a 
still  more  comprehensive  group.  The  strong  point  in  our  position 
lies  in  the  fact  that,  since  variability  is  not  without  limitations,  the 
constancy  in  time  is  absolute  or  real. 

Empiricism  is  again  in  our  favor,  more  so  than  casual  ob- 
servation would  indicate.  The  question  is,  How  do  new  species 
originate?  According  to  NAGELI'S  own  statements,1  it  must  be 
admitted  that  observation  and  experiment  have  not  demonstrated 
the  origin  of  a  species,  neither  due  to  internal  causes  (idioplasm) 


of  the  ancient  Hebrews  in  support  of  bis  theory.     They  certainly  are  not  author- 
ity on  scientific  subjects. — TRANS. 
1  See  ref .  2  on  p.  244. 


246  COMPENDIUM  OF  GENERAL  BOTANY. 

nor  to  external  causes  (influence  of  nutrition,  light,  temperature,, 
mechanical  stimuli,  etc.).  Nageli's  theory  also  differs  from  em- 
piricism in  regard  to  what  external  and  internal  causes  can  pro- 
duce. In  one  important  point  we  agree  with  Nageli;  that  is,  as  to 
the  influence  of  nutrition.  This  factor  is  plainly  under  the  control 
of  direct  observation. 

' '  No  inherited  property,  no  variety,  race,  or  species,  owes  its 
origin  to  nutritive  processes."  It  is  important  to  bear  in  mind 
that  the  same  varieties  may  occur  in  localities  widely  different,  and 
that  two  slightly  different  varieties  may  occur  in  the  same  locality. 
Years  ago  Nageli  also  pointed  out  the  following  general  phenome- 
non. Mountain-plants  transplanted  to  the  valley  lose  their  moun- 
tain habits,  although  they  evidently  lived  among  the  mountains  for 
thousands  of  years.  Climatic  influence  therefore  does  not  produce 
constancy. 

Nageli  assumes  that  the  "  stimuli  "  1  resulting  from  internal 
and  external  causes  are  active  in  producing  new  species,  genera,  etc. 
The  internal  causes  are  supposed  to  lie  in  the  hidden  nature  and 
structure  of  idioplasm.  These  causes  produce  a  continual  progres- 
sive change  in  the  micellar  structure  of  the  idioplasm,  causing  it  to 
become  more  and  more  complicated  and  highly  organized  (principle 
of  perfecting);  primarily,  all  hereditary  transformations  due  to  ex- 
ternal causes  are  the  result  of  idioplasmic  changes.  Progressive 
organization  and  division  of  labor  are  in  general  induced  by  inter- 
nal causes  ;  while  the  specific  constitution  and  variation  in  form, 
organization,  and  division  of  labor,  the  adaptation  to  the  external 
environment,  are  the  result  of  external  causes  (stimuli).  Nageli's 
theory  differs  from  that  of  DARWIN.  According  to  the  latter,  the 
external  causes  act  negatively  in  repressing  or  stamping  out  that 
which  is  not  suited  or  adaptable  (natural  selection  with  struggle  for 
existence).  According  to  Nageli,  the  external  stimuli  act  mechani- 
cally upon  the  micellar  structure  of  the  idioplasm"  to  produce  the 


1  By  "  stimuli"  Nageli  means  those  influences  upon  the  plant-organism  which 
induce   reactionary   effects,  as   mechanical   stimuli,    light,    warmth,    cold.      In 
Nageli's  Abstammungslehre,  p.  102,  there  occurs  a  contradictory  statement  :  most 
climatic  influences  are  classified  with  the  indifferent  influences,  while  on  the  above 
page  warmth  and  cold  are  classed  among  the  effective  stimuli  which  aid  in  form- 
ing hereditary  qualities. 

2  Abstammungslehre,  p.  139. 


REPRODUCTION.  247 

adaptive  changes.  (Further  differences  in  the  theories  of  Nageli 
and  Darwin  will  be  given  below.) 

Nageli  does  not  deny  that  we  do  not  know  how  the  stimuli  act 
upon  the  idioplasm  to  produce  the  required  adaptive  changes.  But 
the  desire  to  formulate  a  theory  of  natural  descent  induced  him  to 
supply  the  necessary  connecting  links  from  fantasy.  For  example, 
he  tries  to  explain  in  what  manner  the  mechanical  tissue-system  was 
in  all  probability  formed.  Let  us  follow  his  argument.  He  says 
that  "  tensions  of  pressure  and  of  pulling  are  strongest  where  the 
mechanical  cells  actually  occur."  Further,  "  tensions  must  predom- 
inate in  the  elongated  cells  of  the  fibro- vascular  bundles,  because  the 
short  parenchyma  cells  with  their  large  intercellular  spaces  cannot  so 
readily  resist  these  tensions,  and  would  become  displaced."  The 
question  now  arises,  Why  are  ring-vessels,  bast,  and  various  cell-wall 
thickenings  formed?  According  to  HABERLANDT  and  AMBRONN, 
the  mechanical  tissue  with  the  vascular  bundles  is  not  always  formed 
from  a  common  cambium.  The  well-established  teaching  of 
SCHWENDENEE,  that  the  mechanical  system  is  independent  of  other 
systems  in  its  arrangement  and  position,  does  not  harmonize  with 
Nageli's  conception.  It  is  also  well  known  that  the  mechanical 
elements  of  the  grass-in  tern  odes  develop  at  the  periphery,  although 
they  are  protected  against  stimuli  of  tensions  by  the  leaf -sheath. 
Further,  in  organs  subject  to  bending,  tensions  are  greatest  at  the 
periphery.  According  to  Nageli,  water-plants  are  evolved  from  or  con- 
verted into  land-plants.  Typical  water-plants  have  a  central  bundle 
of  elongated  elements.  Before  they  can  be  changed  into  land-plants 
it  is  necessary  for  them  to  develop  peripheral  elongated  elements. 
Is  it  probable  that  the  mutual  adaptation  and  arrangement  of 
mechanical  and  assimilating  systems  is  due  to  blind  mechanical 
forces?  Can  any  physiologist  understand  the  complication  which 
arises  when  there  is  established  an  harmonious,  rational  equilibrium 
between  the  position  of  mechanical  and  assimilating  tissues  at  the 
points  of  maximum  tension  and  of  favorable  illumination  ?  This 
much  is  certain,  that  the  mechanical-physiological  theory  of  descent 
can  here  be  no  longer  applied. 

Although  Niigeli  has  allowed  himself  to  be  blinded  by  his  love 
for  the  theory  of  the  natural  origin  of  plants,  yet  his  acute  critical 
powers  are  manifested  in  his  attack  on  DARWIN'S  theory  of  natural 
selection.  Darwin's  theory  of  selection  and  Niigeli's  theory  of  descent, 
which  he  himself  has  designated  as  the  theory  of  direct  cause,  have 


248  COMPENDIUM  OF  GENERAL  BOTANY. 

one  thing  in  common.  It  is,  that  the  present  condition  of  the 
organic  kingdom  was  brought  about  by  individual  variations  and 
the  survival  of  the  fittest  in  the  struggle  for  existence. 

(Competition  or  the  struggle  for  existence  in  both  the  plant  and 
animal  world  is.  according  to  our  opinion,  a  fact,  caused  on  the  one 
hand  by  the  excessive  productiveness  of  the  created  organisms  and 
on  the  other  by  the  constancy  of  the  available  area  of  the  earth's 
surface.  This  competition  is  further  necessary  in  establishing  a 
beneficent  equilibrium  in  nature.) 

In  Darwin's  theory  of  selection,  erratic  variation  is  the  propel- 
ling factor,  selection  is  the  progressing  and  ordering  factor.  Accord- 
ing to  Nageli's  theory,  variation  is  both  the  propelling  and  progres- 
sing factor.  Selection — that  is,  the  survival  of  the  individuals  best 
adapted  to  the  environment — is,  according  to  Darwin,  the  chief 
means  of  evolution  or  perfection  ;  according  to  Nageli,  competition  is 
wholly  without  influence  toward  advancing  from  a  lower  to  a  higher; 
it  only  removes  that  which  is  less  capable  of  existing.  According 
to  this  author,  an  alga  would  have  been  converted  into  an  oak,  an 
amoeba  into  a  mammal,  even  without  competition  ;  only  there  would 
be  in  addition  all  the  descendants  which  have  gone  out  of  existence 
as  the  result  of  competition. 

So  much  concerning  the  difference  between  these  two  theories. 
"We  shall  now  give  some  of  Niigeli's  objections  to  Darwin's  theory 
of  selection  which  we  believe  to  be  important. 

1.  The  undetermined  effects  of  undetermined  causes  presents  so 
much  which  is  accidental  that  this  erratic  variation  in  selection  can- 
not be  harmonized  with  scientific  thought. 

2.  The  crosses  of  varieties  due  to  natural  causes  are  different 
from  those  of  artificially  produced  varieties.     Natural  varieties  fuse 
or  cross  with  difficulty,  and  are  not  changed  by  such  a  process. 

3.  Useful  variations  appear  only  when   the  variations  have  ad- 
vanced to  a  considerable  degree  and  have  affected  a  large  number  of 
individuals,  thus  enabling  them  to  crowd  out  competitors.     But 
since  variations  must  continue  for  a  long  time  on  a  small  scale,  and 
can  exist  only  in  a  few  individuals  during  that  time,  it  is  evident 
that  a  struggle  for  existence  and  natural  selection  cannot  come  into 
play.     The  following  is  an  example  given  by  Niigeli :  the  progeni- 
tors of  our  ruminants  were  hornless;  due  to  variation,  a  few  of 
them  developed  microscopic  horns.     Since  within  the  first  fifty  or 
more   generations   these    horns   must    have   been    functionless   on 


REPRODUCTION.  249 

account  of  their  minuteness,  we  cannot  speak  of  a  selection  and  a 
"struggle."  Furthermore,  crossing  would  continually  tend  to  re- 
move the  incipient  variation. 

4.  Nutritive  influences  do  not  produce  hereditary  changes. 

5.  According  to  Darwin's  theory  of  selection,  the  more  useful 
a  property  of  an  organism  is  the  more  constant  it  must  show  itself 
in  the  process  of  selection  ;  structures  which  do  not  prove  advan- 
tageous must  be  variable.     It  has  been  observed,  however,  that    in 
the  plant  kingdom  the  laws  of  cell-division  and  other  morphological 
characters  are  the  ones  which  prove  to  be  exceedingly  constant ; 
these  certainly  have  nothing  to  do  with  selection.     Here  Nageli 
also  includes  phyllotaxy  (to  be  discussed  later). 

Space  will  not  permit  us  to  enter  into  a  fuller  discussion  of 
Darwin's  theory  and  Niigeli's  objections  thereto. 

Although  Nageli  calls  his  theory  the  "  theory  of  direct  cause,"  it 
does  not  assist  in  elucidating  matters  when  he  assumes  that  it  is 
the  unknown  structure  and  mechanism  of  the  idioplasm  which  causes 
the  evolution  of  the  organic  world.  With  such  total  obscurity  in 
regard  to  our  knowledge  of  idioplasmic  mechanism  we  certainly 
cannot  rationally  speak  of  a  "direct  cause."  Therefore  we  cannot 
recognize  a  theory  of  direct  cause  for  the  existence  of  and  descent  of 
plants  in  the  sense  that  this  existence  is  a  natural  result,  and  not  a 
special  creation.  The  micellar  constitution  of  idioplasm,  which  gives 
rise  to  the  processes  of  life,  must  be  designated  as  a  special  gift  of  the 
Creator.  Nageli  admits  that  the  primordial  plasm  is  converted  into 
idioplasm  by  the  given  (inherent)  molecular  forces.  As  Nageli 
states  that  there  are  causes  inherent  "  by  nature"  in  the  idioplasm, 
so  we  likewise,  from  the  idealistic  point  of  view,  state  that  this  or 
that  happens  according  to  nature.  We,  however,  wish  to  imply 
that  the  natural  laws  as  well  as  matter  itself  are  derived  from 
God,  and  therefore  we  speak  of  the  existence  of  a  special  creation, 
and  not  of  a  natural  necessity,  which  controls  all.  We  will  even  go 
so  far  in  the  use  of  language,  in  so  far  as  we  are  dealing  only  with 
the  natural  laws  of  creation,  that  we  will  not  speak  of  u  miracle," 
although  we  believe  in  the  miraculous  creation  and  preservation  of 
the  universe  by  the  Creator.  We  leave  the  pale  of  science  only 
when  the  sum-total  of  scientific  investigations  fails  us. 

Although  Nageli  has  clearly  shown  the  fallacies  of  Darwin's 
theory,  he  has  allowed  himself  to  fall  into  gross  errors  in  regard  to 
his  own  theory  (for  example,  in  regard  to  the  influence  of  external 


250  COMPENDIUM  OF  GENERAL  BOTANY. 

stimuli,  the  behavior  of  idioplasm).  His  logical  mind,  however, 
finally  led  him  to  that  substance  whose  mechanism  we  cannot 
understand,  but  which  science  has  long  considered  as  the  sustainer  of 
the  various  life-phenomena,  namely,  plasm.  In  this  substance  we 
also  believe  the  forces  to  be  concentrated  which  enter  into  the  phe- 
nomena of  life  and  growth. 

With  idioplasm,  the  structure  and  mechanism  of  which  Nageli 
considers  the  "greatest  mystery  in  the  doctrine  of  descent,"  we  also 
associate  the  miracle  of  creation  ;  we  know  that  "  living  plasm  " 
is  necessary  for  the  existence  of  a  living  cell,  and  hence  for  every 
living  plant.  "Mystery"  and  "miracle"  are  the  two  contrasting 
terms.  Let  our  opponents  not  be  misled :  idealist  and  materialist 
both  fail  to  comprehend  the  natural  causes  of  certain  things.  The 
idealist  knows  from  experience  that  the  thorough  investigation  of 
any  phenomenon  in  nature  will  sooner  or  later  meet  with  conditions 
which  must  be  looked  upon  as  given.  The  materialist  ignores  this 
experience,  does  not  explain  the  "  mystery,"  but  still  maintains  that 
the  ultimate  causes  are  capable  of  a  natural  explanation  without 
miraculous  intervention.  Is  it  not  well  for  the  human  mind, 
which  is  only  a  breath  of  the  creative  Spirit,  to  recognize  one's 
Creator  in  nature  ?  Is  it,  then,  intellectual  weakness  to  acknowl- 
edge the  Almighty  ?  Why  did  Nageli  write,  "  To  deny  spontaneous 
generation  is  to  declare  the  miracle"?  Although  we  declare  the 
miracle,  we  are  stricter  empiricists  than  our  opponents;  we  also 
value  scientific  investigations  which  bring  to  light  truths  which  the 
human  intellect  can  arrive  only  at  after  much  toil. 

APPENDIX. 

The  Life-period  of  Plants. 

1.  The  Schizomycetes  live  about  3-J  hours  on  the  average,  after 
which  the  individual  divides(NAGELi  and  SCHWENDENEE). 

2.  Moulds  and  microscopic  algse  live  from  several  days  to  sev- 
eral months. 

3.  Many  plants  live  one  or  two,  more  rarely  several,  "  vegetative 
periods,"  which  vegetative  period  may  extend  over  a  period  of  from 
J  to  f  of  a  year.     Winter  in  the  temperate  zones  and  the  dry  period 
in  hot  climates  is  the  time  of  vegetative  rest  or  seed -rest.     Accord- 
ingly we  speak  of  annual,  biennial,  or  perennial  plants  (see  p.  158). 


REPRODUCTION.  251 

We  also  find  that  biennial  plants  of  our  climate  become  annual  in 
warmer  climates ;  perennial  plants  of  warmer  climates  sometimes  be- 
come annual  in  our  climate  (Ricinus). 

4.  Tree-like  plants  sometimes  reach  an  old  age.  Of  our  indige- 
nous trees  the  linden,  oak,  pine,  and  yew  may  become  1000  years  old, 
the  yew  even  3000  years.  Among  conifers  the  ages  of  Taxodium 
distichum  (Mexico)  and  Wellingtonia  gigantea  (California)  have 
been  estimated  at  4000  years.  Of  monocotyledons,  Dracaena 
Draco  (Teneriffe)  reaches  the  age  of  several  thousand  years.  The 
climax  of  mass  development  and  age  is  reached  in  Adansonia  digitata 
(Africa),  which  is  said  to  live  6000  years.  At  the  moderate  height 
of  9-12  m.  this  tree  measures  30  m.  in  circumference,  and  has 
branches  15-18  m.  long  (SEUBEKT). 

We  are  in  doubt  as  to  the  exact  age  of  many  subterranean 
rhizomes  and  perennial  plants,  since  we  have  not  actually  observed 
how  long  a  rhizome  may  live. 


PAET  Y. 

THE   GENERAL  CHEMISTRY  AND 
PHYSICS  OF  PLANT-LIFE. 


I    CHEMICAL  PHYSIOLOGY. 

In  the  treatment  of  tissue-physiology  (II,  B)  we  also  took  into 
-consideration  some  very  important  chemical  processes,  such  as  assimi- 
lation and  the  formation  of  albuminous  compounds.  It  now  remains 
for  us  to  consider  the  more  important  features  of  the  general  chem- 
istry of  plants.  (In  the  main  we  will  follow  PFEFFER  and  SACHS.) 

As  a  rule,  the  first  step  in  making  an  analysis  of  a  plant-substance 
is  to  place  the  substance  to  be  examined  in  a  desiccator.  The  deter- 
mination of  the  dry  substance  and  water  of  different  plants  gives 
widely  different  results,  depending  upon  the  conditions  of  develop- 
ment. Ripe  seeds  contain  comparatively  little  water,  the  dry  sub- 
stance constitutes  about  -f  of  the  entire  weight,  while  in  the  germi- 
nating seed,  after  the  reserve  material  has  been  absorbed,  it  is  scarcely 
TV  ;  later  the  weight  of  the  dry  substance  may  again  increase  from 
•J  to  -J.  In  submerged  plants  there  is  of  course  but  a  very  small 
amount  of  dry  substance,  often  less  than  -^. 

On  burning  the  plant  only  a  small  percentage  remains  as  ashes. 
This  important  statement  implies  that  almost  the  entire  mass  of 
the  dry  substance  must  consist  of  combustible  or  volatile  elements 
or  compounds;  the  elements  are  C,  H,  N",  O.  S  remains  in  chemi- 
cal union  with  the  ash,  forming  basic  oxides,  similar  to  the  readily 
oxidizable  P. 

What  are  the  substances  appropriated  by  the  plant,  and  how  are 

252 


THE  GENERAL   CHEMISTRY  AND  PHYSIOS  OF  PLANT-LIFE.  253> 

they  appropriated  ?     What  substances  are  absolutely  necessary,  and 
why? 

C,  H,  O,  N,  also  K,  Ca,  Mg,  P,  and  S,  are  the  elements  of  which 
the  food-substances  are  composed.  Na,  Cl,  and  Si  seem  to  belong 
to  the  group  of  useful  rather  than  necessary  elements.  Among 
fungi,  rubidium  and  caesium  may  be  substituted  for  K  ;  Mg,  Sr,  or 
Ba  for  Ca.  Fungi  may  subsist  without  Fe,  since  they  contain  no 
chlorophyll.  lV[arine-plants  contain  iodine  and  bromine  in  addition 
to  the  elements  mentioned  above. 

Among  plants  0  and  N  are  the  only  elements  which  occur  in 
the  free  state — K  as  a  gas,  O  as  a  gas  and  in  solution  in  water.  The 
remaining  elements  occur  almost  exclusively  as  binary,  ternary,  or 
even  higher  compounds. 

Since  plasm  is  chemically  closely  related  to  albuminous  com- 
pounds, and  since  the  cell-wall  and  starch  consist  of  carbohydrates, 
it  becomes  evident  that  C,  H,  O,  N,  S  are  the  necessary  elements,, 
eventually  also  P. 

Oxygen  alone  enters  into  the  plant-metabolism  as  an  element. 
Iron  enters  the  plant  in  the  form  of  an  oxide  in  solution.  It  occurs 
only  in  small  quantities,  though  it  is  absolutely  necessary  in  chloro- 
phyll-formation and  therefore  also  in  assimilation.  Sulphur  and 
sometimes  phosphorus  are  necessary  in  the  formation  of  albuminous- 
substances.  Potassium  and  calcium  are  also  necessary,  though  their 
true  significance  is  not  understood.  (See  below.) 

According  to  BOUSSINGAULT,  the  free  nitrogen  of  the  air  cannot 
be  utilized  as  food  by  the  plant.  It  is  usually  introduced  into  the 
plant  by  way  of  the  roots ;  not  in  the  free  state,  but  in  the  form  of 
compounds,  such  as  nitrates,  nitric  acid,  and  ammonia  in  solution  in 
water.  In  the  years  1851-1854  Boussingault  apparently  demon- 
strated the  fact  that  when  all  nitrogen-bearing  compounds  were  ex- 
cluded from  the  soil  and  atmosphere,  the  elementary  !N"  did  not  in- 
crease the  nitrogenous  compounds  of  the  plant;  the  plant  would  die 
after  all  the  reserve  nitrogen  in  the  form  of  compounds  had  been  util- 
ized. This  belief  prevailed  until  recent  years,  when  YILLE,  JOULIE, 
ATWATER,  FRANK,  HELLRIEGEL,  and  others  carried  on  experiments 
which  tend  to  prove  that  the  free  nitrogen  of  the  air  may  be  utilized 
by  the  plants.  FRANK  based  his  conclusions  upon  experiments  with 
algae,  fungi,  and  several  phanerogams.  He  has  demonstrated  that 
not  only  are  leguminous  plants  which  bear  root-tubercles  containing 


254  COMPENDIUM  OF  GENERAL  BOTANY. 

fungi  (rhizobia)  capable  of  assimilating  free  nitrogen,  but  also  non- 
leguminous  plants,  as  opposed  to  the  conclusions  of  HELLEIEGEL. 

We  will  now  return  to  the  important  nitrogen-bearing  com- 
pounds. According  to  BOUSSINGAULT,  phanerogams  appropriate 
nitric  acid  more  readily  than  they  do  ammonia ;  for  some  fungi  am- 
monia is  better  suited  than  nitric  acid  (PASTEUR,  A.  MAYEE, 
NAGELI). 

Sulphur  said,  phosphorus  enter  the  plant  in  the  form  of  sulphates 
and  phosphates.1 

The  two  binary  compounds  CO2  and  H2O  supply  the  plant  with 
the  elements  C,  O,  and  H.  CO2  is  almost  exclusively  takon  from 
the  atmosphere,  H2O  almost  exclusively  from  the  soil.  The  process 
of  assimilating  CO2  and  H2O  necessitates  the  presence  of  chlorophyll 
and  the  aid  of  sunlight.  For  each  volume  of  CO2  assimilated  there 
is  liberated  an  equal  volume  of  O.  The  most  common  product  of 
assimilation  among  dicotyledons  is  starch  (amylum),  which  occurs  in 
the  form  of  small  grains.  If  we  consider  C6HJOO5  as  the  formula 
for  this  compound,  the  reaction  may  be  represented  ae  follows : 

6C02  +  5H20  =  C6H1006  +  120. 

In  other  instances  (many  monocotyledons)  a  form  of  sugar  seems 
to  take  the  place  of  the  starch  (see  pp.  122  and  131). 

So  far  we  have  not  been  able  to  follow  the  process  of  assimilation 
in  its  various  phases.  In  the  circulation  of  food-substances  within 
the  plants,  the  processes  of  catabolism,  such  as  converting  starch  and 
cellulose  into  sugar,  decay,  etc.,  are  much  better  known  than  the 
processes  of  metabolism  (assimilation  and  various  processes  of 
transformation.  (See  p.  258). 

At  present  we  have  not  a  clear  understanding  of  the  part  that 
chlorophyll  plays  in  the  process  of  assimilation.  In  the  discussion 
of  the  assimilating  system  we  learned  that  the  influence  of  light 
varied  with  the  wave-lengths  (color) ;  this  relation  was  made  clear 

1  According  to  SACHS,  the  following  is  a  very  satisfactory  culture-fluid  for 
plants: 

Water 1000.0  cu.  c. 

Potassium  nitrate , l.Ogram. 

Chloride  of  sodium .5      " 

Sulphate  of  calcium .5      " 

Sulphate  of  magnesium .5      " 

Phosphate  of  lime  (finely  pulverized) .5     " 

Chloride  of  iron a  few  drops. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PL  ANT- LIFE.  255 

by  ENGELMANN'S  interesting  bacterial  experiments,  which  confirmed 
the  old  theory  of  LOMMEL.  We  shall  now  return  to  the  nitrogenous 
foods. 

The  following  are  natural  sources  of  nitrogenous  compounds. 

1.  The  electric  spark  passing  through  dry  air  produces  NO;  this 
immediately  unites  with  the  O  of  the  atmosphere  and  forms  NO3 ; 
the  latter  unites  with  water  to  form  nitric  acid  : 


O  N02 
H 


NO, 
HO 


2.  In  various  processes  of  combustion  ammonium  nitrite  and 
ummoniurn  nitrate  are  formed  (NH4NO3 ,  NH4NO3). 

3.  Ever  since  animal  creation   the  decay  of  animal  substances 
has  been  the  source  of  important  nitrogenous  compounds,  especially 
NH3  (ammonia).     Connected  with  this  process  of  ammonia-forma 
tion  is 

4.  The  production  of  saltpetre  (potassium  nitrate),  as  follows : 
NH3  takes  up  O  in  the  presence  of  an  alkali ;  that  is,  the  oxidation 
of  NH3  forms  a  nitrate,  as  KNO, ,  NaNO3 ;  the  latter  occurs  very 
plentifully  in  Chili. 

The  formation  of  albuminous  substances  in  the  plant  has  already 
been  discussed. 

Mineral  Food-substances. — The  essential  minerals  are  K,  Ca, 
Mg,  Fe  (S  and  P  were  mentioned  above).  The  agricultural  impor- 
tance of  phosphate  of  lime,  of  the  sulphates,  and  of  the  lime-salts  are 
well  known.  Cl,  Na,  and  Si  are  useful,  though  not  necessary. 

The  true  use  of  K.  that  is,  of  its  compounds,  is  still  unknown; 
it  always  seems  to  be  concerned  in  the  translocation  of  plastic 
materials.  It  is  probable  that  Ca  plays  a  part  in  the  formation  of 
cell-walls.  Mg  seems  to  be  distributed  much  in  the  same  manner 
as  K.  Of  Fe  we  know  definitely  that  it  is  necessary  to  the  forma- 
tion of  chlorophyll.  (This  seems  to  be  the  reason  why  fungi  can  do 
without  it.) 

According  to  the  recent  investigations  of  F.  W.  SCHIMPEB,  Ca 
serves  as  a  vehicle  for  the  mineral  acids,  especially  phosphoric  and 
sulphuric  acid  ;  it  furthermore  prevents  poisoning  by  preventing 
the  accumulation  of  acid  calcium  oxalate.1 


Flora,  1890. 


256  COMPENDIUM  OF  GENERAL  BOTANY. 

With  the  following  enumeration  of  chemical  combinations  and 
mixtures  of  combinations  only  a  few  explanatory  statements  are 
given;  further  detailed  information  in  regard  to  them  has  already 
been  given  and  may  be  referred  to  by  the  aid  of  the  index. 

Carbohydrates,  albuminous  substances,  tannin,  oils,  fats,  wax, 
amides,  resin,  coloring-substances,  ferments. 

Of  the  glucocides  (whose  formation  and  importance  in  the  plant- 
economy  is  still  unknown)  we  may  mention  amygdalin,  salicin,  digi- 
tatin  ;  of  the  bitter  extracts,  lupulin  and  aloin. 

According  to  PFEFFER,  and  more  especially  to  BE  TRIES,  one 
physiological  activity  of  vegetable  acids,  that  is,  their  salts,  is  that 
they  increase  the  hydrostatic  pressure  of  the  living  cell  by  produc- 
ing endosmotic  action. 

The  nitrogenous  organic  com  pounds  of  a  basic  character,  namely, 
the  alkaloids,  must  also  be  mentioned.  They  are  very  frequently 
found  in  the  laticiferous  ducts  of  various  plants.  In  the  milky 
juice  of  the  poppy  (opium-plant)  are  found  thebaine,  morphine,  and 
other  alkaloids;  in  the  bark  of  the  Cinchona,  trees  is  found  the  alka- 
loid quinine'  strychnine  is  found  in  the  seeds  of  Strychnos;  atropine, 
daturine,  hyoscyamine  in  the  Solonacece,  etc.  These  compounds 
have  a  poisonous  effect  upon  the  animal  organism,  and  may  there- 
fore serve  the  plant  as  a  protection  against  the  attacks  of  animals. 

Resins  occur  not  only  in  conifers,  but  also  in  various  exotic 
plants.  Incense  is  a  resinous  product  of  Boswellia  Carterii ; 
myrrh,  of  Commiphora  (Balsamodendron}  Myrrha  (WARMING). 

According  to  HOFPE-SEYLER,  cholesterin,  which  is  widely  dis- 
tributed in  seeds,  is  a  secondary  (catabolic)  product  of  the  albumi- 
noids. 

Leaving  chlorophyll  out  of  consideration,  there  are  many  other 
coloring-substances  occurring  in  the  vegetable  kingdom.  We  will 
refer  only  to  those  usually  associated  with  chlorophyll.  Red, 
brown,  brownish-yellow,  and  blue-green  coloring-substances  are  met 
with  among  various  algse.  Here  also  belong  the  coloring-substances 
of  flowers  and  fruits,  of  fungi,  the  coloring-substances  in  various 
barks.  Examples:  the  kino-red  of  Pterocarpus  Marsupium 
(FLUCKIGER)  and  the  coloring-substances  of  other  woods  (ebony,  etc.). 

In  connection  with  the  characteristic  process  of  carbon-assimila- 
tion it  must  be  impressed  upon  the  beginner  in  the  study  of  plant- 
physiology  that  there  is  a  true  respiration  with  liberation  of  CO2  and 
assimilation  of  O,  besides  the  usual  appropriation  of  CO2  and  libera- 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  257 

tion  of  O.  This  true  respiration  is,  in  general,  necessary  for  the  life 
and  growth  of  plants.  Based  upon  the  investigations  of  BOUSSIN- 
GAULT,  GARREAU,  SACHS,  PASTEUR,  NAGELI,  and  PFEFFEK,  we  may  for- 
mulate our  present  knowledge  in  regard  to  this  subject  as  follows. 

1.  If  we  consider  the  chemistry  of  fermentation  in  plants  (the 
conversion  of  sugar  into  CO2  and  alcohol,  and  other  similar  processes) 
as  "  intramolecular  respiration,"  1  we  may  make  the  general  state- 
ment that  no  plant  can  live  without  respiration. 

2.  Some  of  the  energies  necessary  to  cell-life  -are  due  to  respira- 
tion. 

3.  Oxygen  is  also  necessary  for  the  existence  of  some  fungi  if 
they  are  not  supplied  with  substances  capable  of  undergoing  fer- 
mentation.    Fermentation  enables  them  to  exist  without  the  respi- 
ration of  O ;  without  fermentation  growth  ceases  unless  oxygen  is 
supplied. 

4.  Respiration  continues  as  long  as  the  normal  conditions  of  life 
exist ;  it  is  most  active  in  the  growing  plants  and  growing  parts  of 
plants;  for  example,  during  germination  and  during  the  develop- 
ment of  tubers  and  buds.     Within  certain  limits  respiration  increases 
with  the  rise  of  temperature.     A  direct  influence  of  light  upon  the 
respiration  of  chlorophyll-less  parts  of  plants  has  not  been  observed. 
Chlorophyll-bearing  parts  of  plants  assimilate  only  in  the  presence 
of  sunlight,  but  respire  in  the  dark  as  well  as  in  the  sunlight. 

"  Selection." 

We  usually  speak  of  plants  as  having  the  ability  to  "  select n 
certain  food-substances.  The  true  explanation  of  the  meaning  of 
this  term  is  as  follows.  It  has  been  known  for  a  long  time  that  dif- 
ferent plants  growing  in  the  same  environment  take  up  the  same 
food-substances  in  different  proportions  ;  for  example,  Nympkcea 
alba  and  Arundo  phragmites,  both  of  which  grow  in  water  or  in 
marshy  soil,  and  which  are  therefore  in  contact  with  the  same 
soluble  food-substances,  take  up  SiO2  in  widely  different  proportions. 
The  former  plant  contains  usually  less  than  ^  per  cent  of  silica,  the 
latter  usually  more  than  71  per  cent  (SCHULTZ-FLKETH).  From  un- 


1  According  to  PFLUGER  (1875),  intramolecular  respiration  takes  place  in  an 
atmosphere  free  from  oxygen  with  liberation  of  CO2  due  to  the  breaking  up  of 
compounds  within  the  cell ;  "normal"  respiration  is  accompanied  by  oxygen- 
assimilation. 


258  COMPENDIUM  OF  GENERAL  BOTANY. 

known  causes  inherent  in  the  individual  these  two  plants  require 
different  amounts  of  silica  in  the  building  up  of  the  body-substance 
(deposition  in  the  cell-walls,  etc.).  Due  to  causes  inherent  in  the 
processes  of  osmosis  the  nutritive  cells  of  Arundo  allow  more  SiO, 
to  enter,  because  it  is  continually  removed  and  utilized  elsewhere, 
while  in  Nymphaea  SiO2  is  not  removed  from  the  cell.  As  we 
have  already  learned,  the  living  primordial  utricle  possesses  the 
property  of  being  impermeable  to  certain  substances  in  solution  (as 
sugar,  coloring-substances,  etc.).  This  property  is  due  to  the  in- 
herent peculiarities  of  the  plants  themselves,  and  not  to  any  "  selec 
tive  "  power. 

THE  CYCLIC  COURSE  OF  FOOD-SUBSTANCES. 

The  entire  chemism  of  plants  may  be  diagramatically  repre- 
sented upon  a  circular  line,  dividing  it  into  quadrants  as  follows : 
1,  assimilation  ;  2,  transformation  ;  3,  retrogressive  changes  ;  4,  de- 
composition. 1  and  2  are  metabolic  processes,  3  and  4  catabolic 
(NAGELI). 

COa,  HaO,  and  NH3  (or  HNO3)  figure  as  raw  material  in  the  first 
process  and  again  appear  as  the  final  products  in  process  4,  in  decay, 
fermentation,  etc.  Processes  of  transformation  convert  the  carbo- 
hydrates and  amides  of  process  1  into  more  complicated  chemical 
compounds,  as  cellulose,  albuminoids,  fats,  ethereal  oils,  etc.  Retro- 
gression (3)  works  in  the  opposite  direction  ;  cellulose  is  changed 
into  sugar,  fats  into  fatty  acids  and  glycerine ;  glucocides  are  also 
split  up  into  sugar  and  some  other  compound.  The  products  of  de- 
composition (4)  are  again  the  simpler  compounds  CO,,  HaO,  NH3. 

II.  THE  PHYSIOLOGY  OF  GKOWTH. 

Scientific  botany,  like  other  special  sciences,  finds  its  greatest 
difficulty  in  solving  those  problems  which  lie  nearest  at  hand. 
What  is  growth  ?  Why  must  cells  grow  ?  These  are  questions 
which  the  physics  and  chemistry  of  plants  have  failed  to  answer  sat- 
isfactorily. Growth,  the  specific  manifestation  of  life,  like  all  other 
vegetable  life-phenomena,  can  be  traced  only  to  plasm,  in  which  it 
is  inherent.  There  is  no  mechanics  of  plasm  which  enables  us  to 
deduce  from  the  structure  and  peculiarities  of  plasm  what  actually 
occurs  in  the  growing  cell.  This  statement  is  to  be  emphasized,  be- 


THE  GENERAL  CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  259 

•cause  efforts  have  not  been  wanting  to  explain  the  growth-phe- 
nomena in  cell-life '  from  a  purely  physical  basis.  (See  below.) 

A  cell  must  have  a  certain  degree  of  turgor  as  a  necessary  con- 
dition of  surface-growth ;  hence  turgor  is  a  phenomenon  always 
accompanying  surface-growth.  Frequently  the  ratio  of  growth  pro- 
ceeds parallel  with  the  turgor-force  (DE  TRIES).  Our  knowledge  of 
turgor  is,  however,  far  from  sufficient  to  give  us  a  clear  conception 
of  growth.  There  are  certain  substances  known  to  physiological 
chemistry  which  form  vesicular  deposits,  the  so-called  membranes 
of  precipitation,  as,  for  example,  lime  solution  and  tannin,  sulphate 
of  copper  arid  potassium  ferro-cyanide.  To  these  "  inorganic  cells  " 
(vesicles)  the  "  turgor-growth  "  theory  is  to  a  certain  extent  appli- 
cable :  taking  up  of  water  by  endosmosis  causes  the  artificial  mem- 
brane to  expand  and  finally  to  rupture.  At  this  rupture  the  solu- 
tions within  and  without  at  once  form  a  new  membrane  of  precipi- 
tation ;  this  may  be  repeated  again  and  again.  A  cylindrical  algal 
cell,  however,  differs  very  materially  from  such  artificial  vesicles, 
because  it  has  a  cellulose-membrane  and  plasmic  utricle,  and  the 
cell-wall  can  grow  only  with  the  aid  of  the  plasm.  In  its  chemical 
nature  the  membrane  is  not  merely  a  precipitate  from  the  albumi- 
nous substances  and  water.  Continuing  the  comparison,  one  would 
expect  that  the  cylindrical  cell  would  become  nearly  spherical  in  a 
short  time  because  of  the  equal  expansion  in  all  directions.  Actually 
it  elongates  in  one  direction,  which  indicates  that  a  difference  in  the 
expansion  of  the  cell-wall  in  different  directions  is  one  of  the  con- 
ditions of  cell-growth. 

A.  ZIMMERMANN*  gives  a  brief  summary  of  the  efforts  made  by 
different  authors  to  give  a  mechanical  explanation  of  the  form  and 
position  of  cell- walls.  We  must  estimate  the  work  of  BERTHOLD  and 
ERRERA  especially.  I  say  "  estimate,"  because  it  is  very  important 
that  we  should  not  draw  other  conclusions  than  such  as  really 
follow  from  the  results  of  their  investigations.  According  to  Zim- 
mermann,  the  following  may  be  looked  upon  as  being  established  by 
the  investigations  of  Berthold  and  Errera. 

It  is  an  empirically  derived  rule  rather  than  a  generally  estab- 
lished fact  that  the  cell-wall  during  cell-division  begins  as  a  surface 


1  BERTHOLD,  Studien  iiber  Protoplasmamechanik,  Leipzig,  1886.— TRANS. 
*  Beitrage  zuv  Morphologic  und  Physiologic  der  Pflanzenzelle,  Tiibingen,  1891, 
Heft  2. 


260  COMPENDIUM  OF  GENERAL  BOTANY. 

of  smallest  area.  Although  the  young  cell-aggregates  resemble  the 
vesicles  of  soap-suds  in  their  arrangement  and  in  the  position  of  the 
walls,1  yet  it  must  not  be  assumed  that  this  offers  a  mechanical  ex- 
planation of  cell-wall  formation.  The  attempt  to  explain  the  me- 
chanics of  the  exceptions  to  the  rule  seems  especially  futile.  Further, 
every  anatomist  knows  that  in  the  development  of  plants  and  plant- 
organs  we  are  not  only  concerned  with  cell-aggregates  which  are 
divided  by  surfaces  of  least  area:  the  cell- walls  are  intimately  cor- 
related to  the  form  of  the  organs  as  well  as  to  the  ultimate  function 
of  the  cells.  All  that  we  can  comprehend  of  this  correlation  is  that 
it  serves  a  specific  purpose.  Berthold  himself  does  not  give  an 
exact  mechanical  explanation  of  the  arrangement  of  cell-walls. 

The  growing  cell-wall  (for  example,  of  Spirogyra)  can  not  be 
compared  to  a  liquid  layer,  as  EERERA  has  done ;  the  only  resem- 
blance is  that  of  form.  ZIMMEEMANN  summarizes  NAGELI  and 
SCHWENDENEE'S  (Microskop)  explanations  of  the  causes  of  the  cell- 
forms.  According  to  these  authors  each  cell  and  each  cell-com- 
plex has  a  tendency  to  assume  a  spherical  form  due  to  hydrostatic 
pressure.  Although  this  is  in  harmony  with  the  view  that  the  cell- 
walls  form  surfaces  of  smallest  area,  yet  the  authors  did  not  believe 
that  they  had  discovered  a  fundamental  principle  of  the  mechanics 
of  plasm.  If  we  consider  how  various  the  growth-processes  of 
a  cell  are,  we  will  refrain  from  expressing  the  opinion  that  the  ma- 
jority of  growth-phenomena  can  be  explained  mechanically.  In 
one  case  the  cell  grows  in  length,  in  another  it  expands  into  an 
oogonium  ;  again,  it  branches ;  here  it  may  grow  and  not  divide  ;  it 
may  divide  and  not  grow ;  again,  it  may  grow  in  thickness  only, 
either  locally  or  uniformly ;  etc.  We  have  not  a  thorough  under- 
standing of  a  single  phenomenon  of  growth.2 

Although  there  is  no  satisfactory  explanation  of -growth,  and  no 
mechanics  of  plasm,  there  is  a  physiology  of  growth.  We  shall 
briefly  mention  the  more  important  facts  in  regard  to  it. 


1  PLATEAU'S  "Gleicbgewichtsfiguren." 

2  SCHWENDENER  made  the  following  important  statements :    "  He  who   en- 
deavors to  solve  some  definite  problem  and  who  in  the  course  of  his  investigations 
meets  with  insurmountable  difficulties  has  at  least  found  a  valuable  insight  into 
his  work,  and  his  fellow-workers  will  be  much  indebted  to  him  if  he  makes  known 
his  experience.     But  he  who  does  not  see  the  existing  difficulties  and  who  be- 
lieves he  has  found  the  final  explanation  when  in  reality  only  misunderstood 
processes  are  described,  tends  to  confuse  the  mechanical-physical  investigation 
rather  than  to  promote  it."     (Rectoratsrede,  Berlin,  1887.) 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT- LIFE.  261 

Phenomena  of  growth  and  movement  in  the  vegetable  kingdom 
are  difficult  to  separate.  Naturally  there  is  movement  with  every 
process  of  growth,  though  every  movement  is  not  accompanied  by 
growth. 

A.  ACTIVE  AND  PASSIVE  GROWTH. 

There  is  an  active  as  well  as  a  passive  growth.  The  cambium- 
ring  of  trees  and  the  young  portions  of  roots  show  the  best  examples 
of  active  growth.  The  energy  exerted  by  the  growth-processes  of 
the  cambium  has  not  been  definitely  determined.  From  KRABBE'S 
investigations1  it  would  seem  to  be  considerable  in  trees  with  decidu- 
ous  leaves ;  the  growth-pressure  at  certain  periods  rises  to  fifteen 
atmospheres. 

The  cortex  also  shows  phenomena  of  passive  growth  induced 
by  the  tangential  tension  proceeding  from  the  cambium  (KOPPEN),* 
besides  the  active  growth  observed  in  the  cork-cambium.  A  vis- 
ible result  of  this  tangential  tension  is  the  broadening  of  the 
medullary  rays  in  the  cortex ;  from  this  we  may  conclude  that 
mechanical  tension  can  be  converted  into  growth.  It  is  easy  of 
demonstration  that  an  originally  straight  stem  may  become  perma- 
nently crooked  by  processes  of  passive  growth  when  the  growing 
portion  of  the  stem  is  retained  in  a  crooked  position.  Similar 
processes  occur  in  the  winding  of  climbing  plants  and  tendrils. 
Such  permanent  curvatures  are,  however,  induced  by  special  ener- 
gies which  will  be  discussed  later. 

B.  THE  EESULTS  OF  UNEQUAL  GROWTH. 

According  to  DE  TRIES  (C.  SCHIMPER),  the  term  epinasty  refers 
to  a  relatively  stronger  growth  of  the  upper  side  of  an  organ,  hypo- 
nasty  to  a  stronger  growth  of  the  lower  side.  If  these  inequalities 
occur  in  an  organ  growing  in  length,  curvatures  will  appear;  when 
they  occur  in  organs  growing  in  thickness,  as,  for  example,  in 
horizontal  branches  of  trees,  there  is  produced  a  woody  body  with 
eccentric  pith. 

Unequal  growth  of  different  tissues  in  one  and  the  same  organ 
produces  a  series  of  phenomena  which  will  now  be  briefly  dis- 
cussed. 


1  Abhandl.  der  Berl.  Akademie,  1884. 

2  Nova  Acta  d.  Ksrl.  Leop.— Akad.,  LIII. 


262 


COMPENDIUM  OF  GENERAL  BOTANY. 


Tissue-tension  may  be  mentioned  as  the  first  result  of  unequal 
growth. 

(a)  Tissue-tension. 

To  illustrate  this  phenomenon  a  longitudinal  section  may  be 
cut  from  the  middle  portion  of  a  growing  stem  or  petiole  (L  in 
Fig,  170,  a).  A  vertical  surface  view  of  this  section  is  shown  in  b 
and  c.  The  medulla  m  and  cortex  r  do  not  cease  to  grow  at  the 
same  time  as  the  woody  tissue  h.  In  the  uninjured  organ  this 
difference  must  produce  tensions ;  the  woody  elements  are  passively 
elongated  and  continually  strive  to  contract ;  the  cortical  and  med- 
ullary cells  are  hindered  in  their  growth,  are  compressed,  and  con- 
tinually strive  to  elongate. 


771 


772 


FIG.  170. 

Isolating  the  individual  parts  of  the  section  verifies  the  above 
statement  by  the  shortening  or  elongating  of  the  various  elements. 
For  the  same  reason  the  bisected  organ  curves  outward.  The 
medulla  elongates  more  than  the  cortex  (c).  Increasing  the  turgor 
by  placing  the  section  in  water  will  further  increase  the  curvature. 
Corresponding  phenomena  may  be  observed  in  transverse  sections. 

From  what  has  just  been  stated  it  follows  that  tissue-tensions 
are  produced  by  a  decrease  and  increase  in  the  turgor1  as  well  as  by 
unequal  growth.  The  following  remarks  will  have  a  bearing  upon 
tissue-tension  due  to  turgor.  The  form  of  the  cells  and  their  ex- 
pansibility in  different  directions  influences  the  phenomenon  of  ten- 
sion in  a  high  degree.  In  those  roots  which  become  shortened  in 
the  turgescent  state  and  elongated  in  the  wilted  state,  we  must 


1  According  to  N.  J.  C.  MULLEB,  a  hydrostatic  pressure  of  13^  atmospheres 
can  be  demonstrated  in  the  medullary  cells  of  Helianthm  ;  according  to  AM- 
BRONN,  9-12  atmospheres  in  petioles  of  Fceniculum. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  263 

assume  that  the  cell-walls  are  more  expansible  in  the  transverse 
direction ;  that  is,  the  individual  cells  of  the  root-parenchyma  be- 
come shortened  and  much  expanded  laterally.  The  root-cortex 
remains  passive  during  this  process  of  shortening  and  becomes 
transversely  wrinkled.  The  purpose  of  such  shortening  of  roots  is 
quite  evident.  For  example,  a  rosette  of  radical  leaves  (cataphyi- 
lary)  which,  according  to  their  structure  and  for  mechanical  rea- 
sons, should  remain  near  the  ground  will  thereby  remain  in  the 
same  position,  although  a  short  portion  of  the  stem  below  the  leaves 
elongates  somewhat.  Such  shortening  also  tends  to  hold  the  plants 
more  firmly  in  the  soil.  This  phenomenon  received  a  special  sig- 
nificance from  the  observations  made  by  FITTMANN  (1819).  The 
winter-buds  of  biennial  plants  whose  cotyledons  and  plumules  are 
already  above  the  soil  may  withdraw  them  into  the  soil  on  the 
approach  of  winter.  H.  DE  YEIES  has  explained  the  mechanics  of 
this  phenomenon. 

As  a  second  result  of  unequal  growth  within  an  organ  we  may 
mention 

(£>)  Curvatures. 

Curvatures  of  cylindrical  or  prismatic  organs l  take  place  when 
any  given  longitudinal  portion  of  tissue  elongates  or  shortens  more 
than  does  a  similar  portion  on  the  opposite  side.  It  is  evident  that 
all  such  curvatures  are  not  dependent  upon  processes  of  growth, 
since  shortening  may  also  be  due  to  evaporation  of  water,  and  elon- 
gation may  be  due  to  an  increase  in  the  amount  of  water  taken  up. 
Such  curvatures  do  not  come  under  the  category  of  u  unequal 
growth."  Curvatures  due  to  unequal  growth  are,  however,  of  very 
frequent  occurrence. 

Leaving  out  of  consideration  the  frequently  occurring  foldings 
of  cell- walls,  as,  for  example,  the  "wavy"  epidermis,  the  anatropous 
seed-buds,  etc.,  we  shall  refer  more  particularly  to  those  curvatures 
caused  by  one-sided  exposure  to  light  (heliotropism),  by  the  one- 
sided action  of  gravity  (geotropism),  or  moisture  (hydrotropism). 
These  are  conditions  which  influence  the  growth  of  plants  in  a  high 
degree.  The  significance  of  the  curvatures  mentioned  above  is  very 
evident  when  we  study  the  normal  assimilating  organs,  the  roots, 
etc.  The  leaves  must  assume  a  position  most  favorable  to  the  influ- 


See  NAGELI  and  SCHWENDENER'S  Mikroskop. 


264  COMPENDIUM  OF  GENERAL  BOTANY. 

ence  of  sunlight ;  roots  and  other  subterranean  organs  must  be  con- 
ducted into  the  soil.  The  "  nyctitropic "  curvatures  also  belong 
here. 

To  decide  whether  a  given  curvature  or  phenomenon  of  growth 
is  due  to  the  influence  of  sunlight  or  gravity  we  must  resort  to 
physiological  methods  of  investigation.  The  clinostat  is  the  best 
instrument  to  aid  us  in  deciding  the  question.  This  apparatus  con- 
sists of  a  clockwork  in  which  a  flower-pot  with  a  plant  takes  the 
place  of  the  hand  on  the  dial.  It  is  at  once  evident  that  an  hourly 
rotation  upon  a  vertical  axis  continued  for  days  will  eliminate  the 
influence  of  one-sided  illumination ;  also  that  a  long-continued 
rotation  on  a  horizontal  axis  will  eliminate  the  influence  of  gravity. 
All  that  is  required  is  to  change  the  position  of  the  plant  frequently 
enough,  so  as  not  to  allow  any  perceptible  growth  which  might 
result  from  the  causes  referred  to. 

(c)  Torsion. 

A  third,  and  the  most  complicated,  result  of  unequal  growth 
within  an  organ  is  torsion. 

An  organ  is  said  to  be  twisted  (tordiert)  (NAGELI  and  SCHWEN- 
DENER,3  SCHWENDENEK  and  KRABBE  * )  when  the  originally  longi- 
tudinal lateral  lines  assume  a  spiral  course.  There  are  two  kinds 
of  torsion,  real  and  apparent.  An  apparent  torsion  may  be  caused 
by  curvatures  in  the  successive  planes  of  an  organ  ;  here,  also,  the 
originally  longitudinal  line  takes  a  spiral  course,  but  there  is  no 
transverse  displacement  of  the  cells,  such  as  always  occurs  in  true 
torsion.  There  is  a  form  of  false  "torsion"  noticeable  in  some 
tree-trunks  in  which  the  woody  fibres  take  a  slanting  position, 
caused  by  the  cambial  cells  growing  past  each  other.  The  general 
direction  of  the  trunk  or  branch  is  thereby  not  changed.  In  true 
torsion  the  successive  transverse  disks  glide  upon  each  other.  Both 
forms  of  torsion  are  of  frequent  occurrence  in  the  vegetable  king- 
dom, and  it  is  often  very  difficult  to  determine  quantitatively  what 
is  true  and  what  is  only  apparent  torsion. 

The  following  causes  may  produce  true  torsion  :  (1)  the  more 
rapid  elongation  of  outer  tissue-layers  or  the  shortening  of  inner 
tissue-layers;  (2)  elongation  of  the  cells  in  a  direction  diagonal  to 


1  Microskop. 

2  Tiber  Orientirungstorsionen. 


THE  GENERAL  CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  265 

the  longitudinal  axis  of  the  organ  ;  (3)  the  cells  of  the  entire  organ 
may  tend  to  twist.     All  are  the  result  of  processes  of  growth. 

According  to  Krabbe  and  Schwendener,  the  second  and  third 
causes  producing  torsions  are  active  in  those  adaptive  torsions  which 
bring  dorsiventral  leaves  in  a  favorable  position  with  regard  to  light, 
and  which  cause  zygomorphic  flowers  to  assume  a  suitable  position 
for  being  visited  by  insects.  The  living  plasm  may  be  so  influenced 
by  gravity  or  by  light1  that  the  growth  of  the  cell-wall  of  the  indi- 
vidual cell  may  increase  or  decrease  in  a  direction  diagonal  to  the  lon- 
gitudinal axis.  This  gives  the  individual  cells  a  tendency  to  become 
twisted.  According  to  these  authors,  there  is  therefore  besides  helio- 
tropism  a  heliotortism,  besides  geotropisrn  a  geotortism.  Under  nor- 
mal conditions  gravity  alone  is  active  in  causing  plant-organs  to  assume 
a  definite  position  with  regard  to  its  supporting  axis  or  the  radius  of 
the  earth  ;  but  in  order  that  plant-structures  may  assume  favorable 
positions  in  regard  to  light,  light  and  gravity  must  act  together,  at 
least  in  a  number  of  instances,  while  in  other  instances  light  alone 
is  capable  of  bringing  about  the  necessary  torsion.  I  will  add  a  few 
more  statements  from  the  important  work  of  SCHWENDENER  and 
KRABBE  to  show  how  readily  superficial  considerations  seem  to 
make  it  possible  to  explain  from  a  physical  or  mechanical  basis  the 
most  important  phenomena  of  plant-life. 

1.  An  immediate  causal  relation   between  the  adaptive  move- 
ments of  leaves  and  flowers  on  the  one  hand  and  light  and  gravity 
on  the  other  does  not  exist ;  rather  the  cause  and  effect  are  linked 
together  by  the  unknown  irritability  of  plasm. 

2.  The  authors  mentioned  differ  from  DE  VRIES  in  the  explana- 
tion of  the  phenomenon  due  to  the  amputation  of  leaves.     Among 
many  of  the  plants  with  crossed  opposite  leaf-pairs  (Philadelphus) 
the  leaf-blades  on   the  horizontal    branches  are  brought  into  the 
required  light-position  by  a  torsion  of  the  internode ;  in  addition 
the  leaves  must  also  become  twisted  upon  the  petiolar  axis  to  bring 
the  leaf -blade  into  the  proper  position.     The  active  factor  in  bring- 
ing about  these  movements  is  the  sunlight.     If  the  lower  leaf  of 
the  normal  internode  (not  twisted)  is  removed,  torsion  will  proceed 
as  usual ;  but  if  the  upper  leaf  is  removed  no  torsion  takes  place  in 


1  According  to  Schwendener  and  Krabbe,  there  are  torsions  due  to  the  com- 
bined influence  of  light  and  gravity.  The  manner  in  which  these  two  forces  act 
is  little  understood.  (Compare  the  subsequent  statements  in  the  text.) 


266  COMPENDIUM  OF  GENERAL  BOTANY. 

the  internode  or  in  the  remaining  leaf,  for  such  torsion  would  be 
without  a  purpose.  Further,  the  internode  following  does  not 
become  twisted,  as  might  be  expected,  because  the  new  leaves  are 
already  in  the  proper  lateral  position.  The  weight  of  the  remaining 
lower  leaf  does  not  suffice  to  explain  this  phenomenon,  since  the 
growth-processes  due  to  gravity  would  suffice  to  overcome  the 
weight  of  the  remaining  leaf. 

3.  The  following  is  another  interesting  result  obtained  by 
Schwendener  and  Krabbe.  Theoretically  a  leaf  or  flower  needs,  at 
most,  to  turn  upon  its  axis  180°  in  order  to  bring  it  in  a  favor- 
able position  for  light,  etc.  Careful  observations  have,  however, 
shown  that  long  stems  may  turn  from  500°  to  700°,  while  the 
organs  concerned  retain  their  chosen  adaptive  position.  If,  after 
having  acquired  the  necessary  amount  of  torsion,  the  organ  becomes 
further  twisted  by  processes  of  growth,  it  is  found  that  the  exces- 
sive torsion  is  again  undone  in  the  upper  part  of  the  petiole  or 
peduncle.  This  is  another  interesting  example  showing  that  adapta- 
bility may  be  revealed  by  physical-physiological  investigations,  and 
that  the  teleological  law  is  riot  seriously  shaken,  as  often  happens  to 
the  u  biogenetic  law  "  (HAECKEL). 

C.  MOLECULAR  ORGANIZATION  OF  PLANT-STRUCTURES. 
(APPENDIX  TO  THE  CHAPTER  ON  THE  PHYSIOLOGY  OF  GROWTH.) 

The  following  German  botanists  have  made  a  special  study 
of  this  difficult  subject :  MOHL,  N.  J.  C.  MULLER,  WIESNER, 
DIPPEL,  VON  HOHNEL,  ZiMMERMANN,  AMBRONN,  and  especially 
NAGELI  and  SCHWENDENER  ;  among  specialists  in  other  fields,  v. 
EBNER. 

Some  of  the  problems  relating  to  this  subject  were  touched 
upon  in  the  discussion  of  growth  by  intussusception  (starch- 
grains  and  cell-walls).  The  following  statements  are  based 
upon  the  results  of  the  investigations  of  the  authors  mentioned. 

1.  According  to  Nageli's  micellar  theory  all  bodies  capable 
of  swelling  (in  botany  we  mean  especially  the  starch-grains  and 
cell-walls)  consist  of  micellce  or  aggregates  of  micellae.1  During 


'According  to  Nageli,  chemical  molecules  unite  to  form  molecular  masses  of 
higher  order.  If  this  molecular  union  takes  place  after  a  definite  method  (as,  for 
example,  the  union  of  a  salt  with  water  of  crystallization)  the  resulting  molecular 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PL  ANT- LIFE.  267 

imbibition  each  micella  surrounds  itself  with  a  layer  of  water 
of  a  given  thickness  ;  in  complete  desiccation  the  micellae  lie  in 
contact ;  in  general  their  form  is  polyhedral.  If  water  enters 
between  the  micellae  it  indicates  that  the  attraction  or  cohesion 
between  water-molecule  and  micella  must  be  greater  than  the 
attraction  of  the  micellae  for  each  other  ;  according  to  Nageli 
the  attraction  between  water-molecules  and  micellae  decreases 
more  rapidly  with  the  distance  than  does  the  mutual  attraction 
of  the  micellae  ;  after  a  time  the  latter  will  predominate :  this  is 
the  point  of  maximum  imbibition.  (REINKE'S  experiments  show 
what  enormous  forces  are  exerted  by  the  processes  of  imbibition 
in  such  organized  bodies.  Swelling  of  the  cell-walls  of  Lami- 
naria  indicated  a  pressure  of  forty  atmospheres.) 

2.  Every  normal  cell-membrane  which  has  passed  its  earlier 
stages  of  development  is,  as  a  rule,  doubly  refractive.  According 
to  BRUCKE,  NAGELI,  SCHWENDENER,  and  AMBRONN,  the  cause  of  this 
is  to  be  found  in  the  arrangement  of  the  crystalline,  anisotropic, 
smallest  particles,  the  micellae.  The  membranes  of  typical  me- 
chanical cells  with  normal  extensibility  undergo  no  change  in 
their  optical  behavior  due  to  pressure  or  extension.  Membranes 
of  great  extensibility  when  they  are  subject  to  tension  show  an 
increase  in  the  interference  of  light-rays.  It  may  be  probable 
that  in  the  latter  case  the  optical  difference  is  due  to  a  reticular 
arrangement  of  the  micellae  (SCHWENDENER).  If  such  is  the  case 
it  is  in  favor  of  the  theory  of  "  anisotropic  micellae  "  (MEYER, 
1895). 

Y.  EBNER  and  others,  and  in  partial  agreement  with  them, 
ZIMMERMANN,  suppose  the  cause  of  this  double  refraction  of  some 
cell-membranes,  to  lie  in  the  systematic  arrangement  of  isotropic 
micellae,  without,  however,  being  able  to  give  any  definite  expla- 
nation for  such  systematic  arrangement.  The  evidence  in  sup- 
port of  this  supposition  is  based  upon  the  observation  made  on 
the  above-mentioned  highly  extensible  cells,  without  including 
any  substances  not  pertaining  to  our  subject,  as  bones,  cartilage, 
etc. 

In  reference  to  the  "  molecular  tensions  "  which  VON  HOHNEL 
assumes  to  exist  and  which  are  supposed  to  cause  the  phe- 


mass  is  called  a  pleon  ("  Pleone").     The  micellae  are  either  simple  aggregates  of 
molecules  or  pleon-aggregates. 


268  COMPENDIUM  OF  GENERAL  BOTANY. 

nomena  of  double  refraction,  I  will  add  the  critical  observation 
of  Schwendener.  The  existence  of  unequal  or  one-sided  molec- 
ular tensions  in  the  smallest  particles  of  the  membrane  (the 
micellae)  cannot  be  assumed,  because  we  cannot  conceive  of 
them  as  having  points  of  fixation. 

3.  The  arrangement  of  the  axes  of  the  optically  active  ellip- 
soids of  elasticity  of  the  cell-membrane  always  coincides  with 
morphologically  definable  directions  :  one  axis  is  always  radial ; 
the  other  two  lie  in  the  tangential  plane,  of  course  extending  in 
different  direction.     The  radial  axis  is  usually  the  shortest. 

4.  The   shortest  optical  axis  of  elasticity  always  coincides 
with  the  axis  of  maximum  swelling ;  least  swelling  is  in  the  di- 
rection of  the  optical  axis  of  greatest  elasticity.     If  the  micellae 
are  of  unequal  dimensions  in  the  different  directions  and  are  all 
surrounded  by  equally  thick  layers  of  water,  it  will  be  readily 
seen  that  the  expansion  must  be  less  parallel  to  the  longest  axis 
of  the  micellge  than  to  the  shortest  axis. 


III.    TEMPEKATUEE,    LIGHT,   GEAVITY,  AND    OTHEK 
FACTOES,  IN  THEIE  EELATION  TO  PLANT-LIFE. 

A.  EFFECTS  OF  TEMPERATURE. 

The  discussion  of  the  effects  of  temperature  and  light  will  in 
general  be  based  upon  the  results  of  the  investigations  of  NAGELI, 
SACHS,  PFEFFER,  and  FRANK. 

(a)  Production  of  Warmth  and  Cold. 

Processes  productive  of  heat  and  cold  occur  within  the  plant. 
As  a  result,  plants  give  evidence  of  a  subjective  temperature ; 
that  is,  under  certain  conditions  their  temperature  is  different 
from  that  of  the  surrounding  medium.  Eespiration,  that  is,  the 
conversion  of  hydrogen-  and  carbon-bearing  compounds  into 
CO2  and  H2O,  produces  a  rise  in  temperature.  In  an  extreme 
case  (flowers  of  Aroidece)  the  rise  in  temperature  may  be  15°  C. 
Daring  the  germination  of  barley  the  temperature  also  rises,  as 
is  well  known.  Evaporation  of  moisture  from  the  plant  tends  to 
reduce  the  temperature. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  269 

(b)   The  Effect  of  Temperature  upon  Plant-life. 

As  every  chemical  process  takes  place  in  a  certain  tempera- 
ture, so  likewise  are  the  various  life-processes  of  plants  depend- 
ent upon  certain  temperatures ;  among  different  plants  the  same 
life-process  may  be  dependent  upon  different  temperatures. 
However,  the  temperature  suitable  to  a  given  process  may  vary 
considerably,  so  that  we  usually  speak  of  a  minimum,  optimum, 
and  maximum  temperature.  According  to  SACHS,  these  three 
"cardinal  points  "  for  the  germination  of  our  cereals  are  approx- 
imately at  0°,  28°  (optimum),  and  40°  C. 

In  reference  to  experimental  physiology  it  may  be  mentioned 
that  there  are  special  apparatus  for  the  determination  of  the 
rate  of  growth  within  definite  periods  of  time.  Such  are  the 
auxanometers  of  SACHS,  WIESNEE,  and  BARANETZKY. 

Below  the  optimum  the  curve  of  growth  rises  and  falls  with 
the  temperature-curve.  The  curves  at  least  tend  in  the  same 
general  direction,  though  they  may  not  be  parallel.  It,  however, 
requires  great  care  to  determine  the  influence  that  each  individ- 
ual factor  has  upon  growth.  Some  observations  in  regard  to 
these  difficulties  will  be  in  order.  When  observing  the  influence 
of  a  constant  temperature  upon  the  growth  of  a  plant  which  is 
at  the  same  time  exposed  to  a  variable  illumination,  for  example 
growth  during  day  and  night,  we  encounter  a  complication 
(SACHS  ').  The  shoot-axis  of  Dahlia,  for  instance,  shows  a 
maximum  growth  in  the  early  morning ;  in  the  afternoon  a  reduc- 
tion ;  before  sunset  another  increase.  It  is  evident  that  in  this 
case  the  growth-curve  would  not  extend  parallel  with  the  temper- 
ature-curve. According  to  the  observations  made  by  SACHS  and 
BARANETZKY,  there  is  a  periodicity  of  growth  independent  of 
temperature  and  light,  which  is  manifest  in  a  rise  and  fall  extend- 
ing over  a  variable  period  of  time.  -  The  most  important  and 
most  general  phenomenon  in  this  periodicity  due  to  internal 
causes  is  the  grand  period  of  growth  (Sachs) :  each  transverse 
zone  of  a  root,  of  a  stem,  etc.,  begins  to  grow  slowly,  then  grows- 
more  rapidly,  and  after  having  reached  the  maximum  gradually 
decreases  until  it  ceases  to  grow  entirely.  Such  periodicity  is. 
not  due  to  external  causes. 


1  Vorlesungen,  p.  680. 


270  COMPENDIUM  OF  GENERAL  BOTANY. 

Effects  of  Extreme  Temperatures. — Seeds  of  plants  in  a  dry 
state,  may  withstand  very  low  temperatures.  The  same  is  true 
of  spores,  yeast-cells,  and  the  Schizomycetes.  Well-dried  seeds 
may  resist  a  temperature  of  120°  C.  without  losing  the  power 
of  germination.  "  Sterilization  "  in  bacteriology  requires  that 
liquids  should  be  boiled  for  hours  in  order  to  kill  all  the  germs 
of  fungi,  or  exposed  to  dry  heat  at  130°  to  140°  C.  for  a  longer 
period. 

In  general  it  may  be  stated  that  plants  and  parts  of  plants 
with  a  low  percentage  of  water  will  withstand  the  extremes 
of  temperature  better  than  succulent  plants.  Lichens,  for 
example,  will  resist  the  extremest  cold  of  winter.  Winter  wheat, 
without  being  covered  by  snow,  will  resist  a  temperature  of 
— 10°  C.,  or  even  lower  ;  Coleus  is  killed  by  a  temperature  of  1°  to 
1.5°  C.  Succulent  plant-portions  of  various  phanerogams  are 
killed  by  a  temperature  of  45°  to  50°  C. 

Freezing  does  not  always  kill  the  plant ;  death  sometimes  re- 
sults during  the  process  of  thawing.  If  this  process  is  allowed 
to  proceed  slowly  the  life  of  the  plant  may  continue.  Freezing 
inhibits  turgescence,  that  is  the  water  within  the  cells  escapes 
into  the  intercellular  spaces.  As  a  rule,  ice-formation  begins 
outside  of  the  cells,  in  the  intercellular  spaces,  when  the  temper- 
ature sinks  slowly  to  —5°  C.,  or  even  lower.  A  sudden  and  exces- 
sive fall  in  the  temperature  causes  rupturing  of  the  cells  and 
tissues,  due  to  the  pressure  of  the  rapidly  forming  ice-crystals. 
When  the  process  of  thawing  is  sufficiently  slow  the  water  is 
again  taken  up  by  the  remaining  living  cells.  However,  accord- 
ing to  FRANK  and  MULLER-THURGAU,  death  may  result  during  the 
process  of  freezing. 

B.  EFFECT  OF  LIGHT. 

(a)  Production  of  Light. 

Many  plants  and  parts  of  plants  are  luminous  in  the  dark  ; 
for  example,  certain  fungi  (bacteria).  Since  this  phenomenon 
ceases  on  the  exclusion  of  O,  it  is  in  all  probability  a  process  of 
oxidation. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE. 


(b)  Influence  of  Light  upon  Plant-life. 

The  difficult  problem  which  we  will  encounter  in  this  chapter, 
as  well  as  in  the  corresponding  chapter  on  gravity,  is  that  the 
same  causes  do  not  produce  the  same  effects  in  all  living  cells, 
but  rather  produce  effects  which,  to  external  appearance  at 
least,  are  directly  opposite.  The  evidence  that  the  principle  of 
adaptation  is  the  controlling  factor  in  such  phenomena  is  so 
conclusive,  that  the  investigations  which  stand  at  the  very  height 
of  purely  scientific  and  causal-mechanical  methods  lead  to  the 
same  conclusion. 

Here  also  we  must  speak  of  a  minimum,  optimum,  and  maxi- 
mum effect  of  light  upon  the  various  organs  and  life-processes. 
Elementary  physics  teaches  us  that  we  not  only  have  to  deal 
with  the  effect  of  various  light-intensities,  but  also  with  the  effects 
of  different  ivave-lengths  (hence  colors). 

In  general,  chlorophyll-formation  requires  less  light  than 
chlorophyll-activity  (assimilation)  :  the' former  process,  the  turn- 
ing-green of  plants,  may  even  take  place  in  the  dark ;  for  exam- 
ple, in  ferns  and  in  the  seedlings  of  conifers.  Coloring-sub- 
stances of  flowers  may  also  be  formed  in  the  dark,  provided  the 
necessary  assimilated  substances  are  present,  or  their  formation 
made  possible  (SENEBIEE,  DE  CANDOLLE,  SACHS).  Sachs  further 
found  that  the  floral  buds  of  Tropceolum  require  the  ultra-violet 
rays  for  their  development.  With  the  aid  of  these  rays  the 
flower-forming  substances  would  be  produced  in  the  green  leaves 
(Sachs).  The  relation  of  wave-length  to  the  function  of  assimi- 
lation has  already  been  explained  (Part  II,  B).  The  highest 
optimum  (there  are  two  maxima  of  assimilation),  according  to 
ENGELMANN,  lies  in  the  red  spectrum.  The  rays  passing  through 
ammoniacal  oxide  of  copper,  hence  the  highly  refrangible  rays, 
are  most  active  in  the  phenomena  of  growth  and  plant  move- 
ment (movement  of  chlorophyll,  heliotropism).  They  resemble 
more  nearly  the  activity  of  normal  daylight. 

Effects  of  Abnormal  Illumination  and  the  Conclusions  derived 
therefrom. — Plants  which  are  normally  subject  to  the  change  of 
day  and  night  on  exposure  to  continuous  darkness  show  a 
variety  of  effects  upon  the  different  organs.  The  pathological 
phenomena  usually  depend  upon  deficient  nutritive  changes. 


272  COMPENDIUM  OF  GENERAL  BOTANY. 

Let  us  consider  the  behavior  of  the  potato-plant,  according  to 
the  observations  of  Sachs.1  The  young  shoots  (the  "  eyes  ")  of 
the  tuber  require  darkness  for  their  growth ;  light  hinders  their 
development  in  a  remarkable  degree  ;  later  the  different  mem- 
bers and  leaf-organs  developing  from  them  must  have  sunlight 
for  their  normal  development.  The  shoots  first  named  are 
adapted  to  grow  in  darkness  ;  from  them  the  tubers  are  devel- 
oped. Many  other  subterranean  organs  do  not  show  this  sen- 
sibility to  light.  Let  us  consider  two  simple  experiments.  1. 
Observe  the  growth  of  seedlings  and  shoots  in  permanent  dark- 
ness. 2.  Place  one  part  of  a  plant  in  the  dark,  while  the  remain- 
ing parts  are  normally  illumined  (according  to  the  experiment  by 
SACHS).  In  these  cases  growth  in  the  dark  can  take  place  only  at 
the  expense  of  the  reserve-materials  or  of  food-substances  formed 
in  adjacent  tissues  under  normal  surroundings.  In  case  the 
seedlings  and  shoots  show  a  rapid  growth  of  the  axial  organs 
they  become  abnormally  elongated,  with  usually  slight  develop- 
ment of  the  mechanical  cells.  The  leaves  remain  dwarfed,  but 
this  is  not  directly  due  to  the  lack  of  sunlight,  for  case  2  shows 
that  leaves  may  develop  on  the  darkened  plant  portion,  though 
they  may  not  be  of  normal  size.  The  darkened  portion  (2) 
may  even  develop  normally  colored  flowers  and  fruit.  In  both 
cases  and  in  general  it  may  be  stated,  that  leaves  developed  in 
the  dark  are  devoid  of  chlorophyll ;  they  are  said  to  be  "  chlorotic," 
or  etiolated* 

From  the  study  of  these  pathological  changes  and  the  peculiar 
differences  associated  therewith  we  are  enabled  to  understand 
their  teleological  significance.  Cotyledons  which  normally  re- 
main under  ground,  and  therefore  do  not  become  very  much 
elongated  in  the  hypocotyledonous  stem-portion,  do  not  show 
any  abnormal  elongation  in  permanent  darkness.  On  the  other 
hand  seedlings  whose  cotyledons  are  normally  raised  above  the 
soil  show  the  described  elongation  when  growing  in  the  dark. 
Again,  not  all  foliage-leaves  remain  small  in  the  dark ;  many 
blade-like  monocotyledonous  leaves  become  abnormally  long 
and  slender  in  the  dark.  This  is  also  true  of  the  leaves  of  the 
onion  ;  by  their  elongation  they  are  enabled  to  rise  above  the 


1  Vorlesungen,  p.  650. 

s  SACHS,  Abhandhmgen  iiber  Pflanzen-Phys.  p.  194.     (1892.) 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  273 

ground  from  their  low  position,  and  may  pusli  their  way  out  of 
the  leaf-sheaths. 

The  following  phenomena  come  under  the  same  teleological 
category.  1.  Many  plants  show  little  or  scarcely  any  growth  in 
the  dark.  2.  Hoots,  in  general,  grow  more  rapidly  in  the  dark 
than  in  the  light.  3.  Many  fungi  can  grow  only  in  the  dark. 
Of  the  latter  we  know  that  light  is  not  a  factor  in  their  nutrition. 
In  the  case  of  roots  we  know  from  observation  that  their  normal 
growth  takes  place  in  the  dark.  In  regard  to  1,  many  cases 
are  yet  not  satisfactorily  explained ;  but  it  is  very  clear  from 
physiological  evidence  that  many  fern-spores  require  light  for 
their  germination  (BORODIN  and  others) ;  this  is  also  true  of  the 
spores  of  some  mosses  (BORODIN,  LEITGEB).  In  these  cases  the 
products  of  germination  can  only  continue  their  growth  with  the 
aid  of  sunlight. 

Phototonus  is  the  term  applied  to  the  normal  reaction  of 
plants  to  the  rhythmic  change  of  light  and  dark  (day  and  night). 
A  longer  or  shorter  exposure  to  dark  will  temporarily  destroy 
this  phototonic  condition,  producing  a  transitory  state  of  rigidity 
(Dunkelstarre,  SACHS). 

In  general  it  may  be  stated  that  the  phototonic  plants,  hence 
normal  plants,  exposed  to  the  daily  change  of  light  grow  more  rapidly 
during  the  dark  period  (night),  tvhile  uniform  illumination  (dayy 
retards  the  growth.  Special  cases  with  explanations  have  already 
been  cited. 

Intimately  associated  with  phototonus,  that  is,  the  condition 
produced  by  alternating  light  stimuli,  is  the  phenomenon  of 
"  sleeping  "  and  "  waking  "  (opening  and  closing)  of  leaves  ;  in 
other  words,  the  nyctitropic  movements.  According  to  CHARLES 
DARWIN,  the  purpose  of  this  movement  is  to  reduce  the  radiation 
of  heat  during  cold  nights.  Among  flowers  it  is  usually  a  pro- 
cess of  closing,  and  also  serves  the  function  of  protecting  the 
internal  organs.  These  movements  are  not  always  curvatures, 
but  sometimes  also  torsions.  We  will  here  consider  only  the 
simple  curvatures. 

The  mechanics  of  this  movement,  of  which  the  following  are 
the  essential  features,  is  only  in  part  explained.  Groivth  processes 
of  the  joints  or  motile  organs,  or  of  the  nyctitropic  organs  with- 
out motile  organs,  are  not  the  only  conditions  producing  this 
phenomenon ;  turgor-changes  are  the  essential  factors.  In  the 


274  COMPENDIUM  OF  GENERAL  BOTANY. 

motile  organ  of  the  Oxalis-lesii  there  is  an  upper  and  a  lower 
cushion  of  cells  with  an  intermediate  elastic  vascular  tissue- 
bundle.  In  the  dark  the  turgor  and  volume  of  the  entire  organ 
increases  ; '  in  the  light  it  decreases.  Although  the  decrease 
and  increase  in  the  volume  of  the  two  cushions  of  cells  begins 
at  the  same  time,  it  does  not  proceed  equally  fast,  so  that  in  the 
dark  the  swelling  of  the  upper  cushion  proceeds  more  rapidly, 
causing  the  leaf  to  turn  downward.  On  exposure  to  light  the 
turgor-difference  is  again  manifest,  but  in  the  inverse  order  ;  that 
is,  the  upper  cushion  loses  its  turgidity  more  rapidly,  causing 
the  leaf  to  be  turned  upward  by  the  more  turgid  lower  cushion. 
The  explanation  of  this  phenomenon  becomes  still  more  difficult 
and  complicated  by  the  so-called  "  after  effects."  A  nyctitropic 
plant  previously  exposed  to  the  changes  of  day  and  night,  when 
placed  for  days  in  either  continuous  dark  or  continuous  light,  still 
continues  to  produce  to-and-fro  movements.  These  movements, 
which  are  as  yet  unexplained,  unite  with  the  movements  due  to 
the  change  of  illumination  (BBiiCKE,  PFEFFEB,  MILLABDET,  SACHS). 

The  common  garden  bean  furnishes  a  good  example  of  this 
phenomenon.  It  need  hardly  be  mentioned  that  we  cannot  see 
the  causal  relation  between  the  variations  in  turgor  and  the 
variations  in  illumination.  We  can  only  establish  the  fact  of 
the  existence  of  such  relative  variations. 

One-sided  illumination  acts  in  such  a  manner  upon  the  longi- 
tudinal growth  of  an  organ  that  the  side  exposed  to  the  light  is 
retarded  in  its  growth,  thus  producing  a  curvature  toward  the 
light.  Most  shoots  and  leaves  show  such  positive  heliotropism. 
One-sided  illumination  may  also  have  the  opposite  effect ;  that 
is,  the  side  turned  toward  the  light  increases  in  growth  and  the 
organ  is  turned  away  from  the  light.  This  phenomenon,  which 
is  called  negative  heliotropism,  occurs  in  the  climbing  shoots  of 
ivy,  in  many  aerial  roots,  and  in  some  subterranean  roots. 

To  give  a  causal-mechanical  explanation  of  this  phenomenon 
is  also  impossible.  We  feel  certain  that  it  is  due  to  the  behavior 
of  the  living  cell-plasm ;  the  question  of  the  cause  of  such  be- 
havior is  quite  another  thing.  Many  investigators  will  of  course 
be  imbued  with  the  idea  that  a  teleological  principle  also  con- 
trols these  relations,  since  this  principle  forms,  so  to  speak,  the 


JIn  this  case  the  expression  "sleep"  does  not  mean  relaxation. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  275 

keystone  of  our  knowledge  already  gained  and  that  for  which 
we  are  striving.  A  similar  difficulty  in  finding  a  causal  explana- 
tion is  met  with  in  negative  and  positive  geotropism,  which  we 
shall  now  discuss. 


C.  INFLUENCE  OF  GKAVITY. 

The  plant  kingdom  is  subject  to  the  continuous  influence  of 
gravity.  Light  and  temperature  have  their  variations  in  the 
change  of  day  and  night  and  in  the  seasons  of  the  year.  Gravity 
is  a  constant  factor  and  has  a  great  influence  on  plant-life. 

If  a  growing  primary  root  is  placed  horizontally,  it  will  at 
once  begin  to  curve  downward  at  the  growing  part,  due  to  the 
more  active  growth  of  the  upper  side.  A  portion  of  the  stem 
(growing  shoot)  or  the  base  of  the  leaf-sheath  of  a  grass-inter- 
node  *  placed  horizontally  will  curve  upward  because  of  the 
more  rapid  growth  of  the  lower  side.  This  is  the  so-called  posi- 
tive and  negative  geotropism. 

It  can  readily  be  shown  that  it  is  gravity  which  causes  the 
downward  growth  of  roots  (positive  geotropism)  and  the  up- 
ward growth  of  stems  (negative  geotropism).  If  the  centrifugal 
machine  is  employed  to  counteract  the  earth's  gravity,  it  is 
found  that  the  root  grows  outward  and  the  stem  grows  in  the 
opposite  direction  toward  the  centre  of  rotation. 

Secondary  roots,  branches,  and  leaves  are  controlled  by  other 
factors,  since  they  grow  in  a  diagonal  or  horizontal  direction 
under  the  influence  of  gravity.  According  to  SACHS,  the  latter 
organs  are  said  to  be plagiotropic,  in  distinction  to  the  orthotropic 
stem  and  primary  root.2  SACHS  emphasizes  the  fact  that  dor- 
si  ventral  organs  are  plagiotropic ;  this  one  would  expect  when 
considered  from  the  standpoint  of  advantageous  adaptability. 
The  horizontal  position  is  certainly  more  suitable  for  organs 
with  one  side  adapted  to  light  and  the  other  to  comparative 
darkness.  According  to  the  same  author,  all  orthotropic  organs 
have  a  radial  structure  (see  p.  166)  which  corresponds  to  the 


1  Concerning  this  behavior  of  leaf -sheaths  and  nodes  of  Gramincce  see  Part  II, 
B,  Function  V. 

2  Sachs  also  applies  these  terms  to  a  similar  behavior  of  plants  in  response  to 
light-effects. 


276  COMPENDIUM  OF  GENERAL  BOTANY. 

function  of  an  equally  illumined  stem  as  well  as  to  that  of  the 
root,  which  serves  to  fasten  the  plant  to  the  soil  and  to  take 
up  soluble  food-substances  from  all  sides  by  means  of  the 
numerous  secondary  roots  and  rootlets. 


D.  ELECTRICITY.    MOISTURE.  WATER-CURRENTS.  RADIATING  HEAT. 

Electrical  Currents  Produced  by  Plants. — Electrical  currents 
have  been  demonstrated  in  the  plant-body  ;  also  variation  in 
these  currents.  Movements  of  water-currents  in  the  plant  are 
supposed  to  be  the  cause  of  the  variations  in  the  electrical  cur- 
rents (RANKE,  VELTEN,  MUNK,  KUNKEL).  The  significance  of  these 
currents  is  unknown. 

The  following  are  some  of  the  effects  of  the  electrical  currents 
upon  the  processes  of  plant-life,  though  no  important  significance 
has  yet  been  ascribed  to  this  knowledge.  Electrical  discharges 
cause  cessation  of  the  movements  of  the  swarm-spores  of 
Vaucheria  (UNGER) ;  they  cause  cessation  of  the  motion  of  the 
granules  in  streaming  protoplasm  (KiiHNE,  NAGELI,  and  SCHWEN- 
DENER)  ;  they  also  cause  closing  of  the  stoma  (N.  J.  C.  MULLER), 
perhaps  due  to  changes  in  turgor.  Strong  currents  may  kill  the 
cells.  At  this  point  it  is  well  to  mention  BRUNCHHORST'S  galvan- 
otropism.  Roots  growing  in  water  incline  toward  the  negative 
electrode  with  weaker  currents.  Stronger  currents  cause  the 
roots  to  incline  toward  the  positive  pole,  due  to  pathological  influ- 
ences (ELVFING). 

The  observation  made  by  SACHS  that  growing  root-tips  will 
turn  toward  a  moist  body  (positive  hydrotropism)  is  of  physiolog- 
ical importance.  The  same  author  observed  negative  hydrot- 
ropism in  stems  of  seedlings  and  in  the  spore-bearing  hyphse 
of  the  Phycomyces. 

Growing  roots  of  Zea  Mays  turn  toward  the  current  of  run- 
ning water  (JoNSSON,  rheotropism).  According  to  WORTMANN,  some 
growing  plant-portions  turn  toward  a  source  of  warmth  (positive 
thermotropism),  while  others  turn  away  (negative  thermotropism) : 
examples  for  both  are  found  among  young  stems  of  various 
plants.  In  one  and  the  same  root  a  temperature  below  27.5  °  C. 
produced  positive  thermotropism  ;  a  higher  temperature  pro- 
duced negative  thermotropism. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  277 


IV.  THE  PHYSIOLOGY  OF  PLANT-MOVEMENTS. 

A.    CLASSIFICATION    OF    MOVEMENTS    ACCORDING  TO   CAUSE.    THE 
OUTWARD  MANIFESTATION  OF  SOME  MOVEMENTS. 

The  consideration  of  the  outward  manifestation  of  movements 
in  plants  does  not  aid  us  in  forming  a  rational  classification  of 
the  same.  The  following  will  explain. 

In  general,  nutation  implies  the  curvature  of  an  organ.  To 
bring  this  about  it  is  necessary  that  one  side  should  always  be 
relatively  longer  or  shorter  than  the  opposite  side.  Elongation 
of  tissues  (cells)  may  be  due  to  growth  or  to  the  taking  up  of 
water  without  growth.  Shortening  is  usually  due  to  changes  in 
the  amount  of  water  present,  but  may  also  be  due  to  other  causes. 
If  the  line  of  maximum  expansion  changes  from  side  to  side 
(with  or  without  growth),  it  will  cause  the  organ  to  move  back 
and  forth  like  a  pendulum.  The  leaflets  of  Hedysarum  gyrans 
describe  elliptical  curves  (without  growth). 

When  the  longitudinal  axis  of  maximum  growth  or  maximum 
expansion  remains  neither  on  one  side  nor  alternates  from  one 
side  to  the  other,  but  rotates  or  ivinds  about  in  the  organ,  it  pro- 
duces what  is  known  as  ctrc^mnutation.  The  organ  is  thereby 
carried  around  in  a  circle ;  the  growing  tip  describes  a  spiral 
line. 

Torsions  also  belong  to  the  important  phenomena  of  move- 
ment. They  may  also  be  the  result  of  a  variety  of  causes.  The 
locomotor  movements  are  characteristic  because  of  their  external 
peculiarity  :  entire  plants  or  parts  of  plants  may  move  about. 
The  movements  of  entire  plants  may  be  explained  mechanically 
when  cilia  can  be  demonstrated,  as  in  various  swarm-spores  and 
bacteria ;  if  cilia  are  wanting,  as  in  Diatomacece,  Myxomycetes, 
etc.,  it  is  difficult  or  impossible  to  explain  the  motion.  As 
motion  of  parts  of  plants  the  movement  of  chlorophyll  and  plasmic 
motion  may  be  mentioned  as  an  example.  The  former  we  can 
comprehend  at  least  from  a  teleological  point  of  view.  (See  Func- 
tion VI  in  the  Physiology  of  Tissues,  Part  II,  B.)  The  causa 
efficiens  as  well  as  the  causa  finalis  of  plasmic  movement  is  un- 


278  COMPENDIUM  OF  GENERAL  BOTANY. 

known.1     Cells  of  the  Characece  show  the  streaming  movement 
of  plasm  very  beautifully. 

With  these  general  remarks  on  some  of  the  more  important 
movements  met  with  in  the  vegetable  kingdom  we  may  group 
them,  according  to  cause,  as  follows. 

1.  Locomotor  movements  due  to  causes  inherent  within  the 
protoplasm.     It  were  better  to  say  that  the  cause  or  causes  are 
unknown. 

2.  Purely  mechanical  movements  due  to  variations   in  the 
turgor  of  living  cells  or  to  absorption  or  loss  of  water  by  dead 
cell-walls.     We    will   name   them    collectively    "  hygroscopic " 
movements. 

3.  Autonomous  or  spontaneous  movements,  often  producing 
extensive  changes  in  form  and  position,  are  also  due  to  internal 
causes,  such  as  processes  of  growth. 

4.  Irritable  movements  (induced  movements). 
We  will  briefly  discuss  movements  2,  3,  and  4. 

B.  HYGROSCOPIC  MOVEMENTS. 

The  term  hygroscopic  applies  to  the  unequal  gain  and  loss  of 
water  by  dead  as  well  as  by  living  cells.  Under  the  category  of 
hygroscopic  movements  belong  the  opening  of  sporangia  and 
anthers  as  well  as  fruits  for  the  purpose  of  ejecting  the  seeds, 
spores,  etc.  A  number  of  these  cases  have  been  elucidated  by 
the  investigations  of  SCHINZ,  SCHRODT,  ZIMMERMANN,  STEINBRINCK, 
EICHHOLZ,  ZOPF,  and  others.  Since  these  movements  have 
already  been  more  or  less  explained  in  the  chapters  on  repro- 
duction, I  will  here  limit  myself  to  the  following  statement. 
Hygroscopic  movements  are  usually  due  to  the  difference  in  the 
power  of  imbibition  possessed  by  the  various  tissues  and  tissue- 
layers.  Visible  structural  differences  often  indicate  the  differ- 
ence in  the  power  of  imbibition.  The  dynamical  cells  evidently 
come  into  play  here  (ZIMMERMANN).  These  cells  have  a  moder- 
ately thick  wall,  with  approximately  horizontal  rows  of  micella 
which  are  capable  of  shortening  considerably  on  drying,  much 


1  Attempts  have  been  made  by  various  investigators  to  explain  the  phenomena 
of  protoplasmic  movement,  but  so  far  not  very  successfully.  Ghemism  and  surface- 
tension  of  liquids  are  perhaps  factors  in  such  movement.  See  BBRTHOLD'S  Proto- 
plasmamechanik. — TRANS. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  279 

i 

more  so  than  cells  with  micellae  placed  longitudinally.     Such 

cells  we  have  learned  to  know  as  the  specific  (dynamostatic)  me- 
chanical cells.  Should  these  different  cells  occur  on  opposite 
sides  of  an  organ  it  will  evidently  result  in  bringing  about  a 
curvature.  The  umbels  of  various  Umbelliferce  (Daucus,  etc.) 
show  these  different  cell- structures  and  the  resulting  behavior 
very  clearly  (O.  KLEIN). 

As  already  indicated,  there  are  cases  in  which  the  turgor  of 
living  cells  causes  the  expansion  of  tissue-layers,  as,  for  example, 
in  the  seed-coats  of  Impatiens. 

To  the  category  of  purely  mechanical  or  hygroscopic  move- 
ments belong  many  teleological  phenomena  having  no  bearing 
on  reproduction,  as,  for  example,  the  rolling-in  or  folding  of 
leaves  to  guard  against  excessive  evaporation,  frequently  notice- 
able in  plants  of  the  desert  (TscHiRCH,  VOLKENS,  and  others).  In 
these  cases  the  mechanical  action  producing  the  required  move- 
ment is  also  due  to  changes  in  the  turgor  of  living  cells  or  to 
changes  in  the  power  of  imbibition  of  the  cell-membranes.  Here 
belong  the  movement  of  the  guard-cells  of  the  breathing-pores, 
evidently  due  to  changes  in  turgor  (see  the  mechanics  and  an- 
atomy of  stomata).  Finally,  it  should  be  remembered  that  the 
purely  mechanical  movements  may  induce  either  simple  curva- 
tures or  torsions.  (The  penetration  of  the  seed  of  Erodium 
gruinum  into  the  soil  is  due  to  a  process  of  torsion.) 

C.  AUTONOMOUS  MOVEMENTS. 

These  are  due  to  internal  causes  and  may  recur  periodically, 
or  they  may  occur  only  once  or  a  few  times  during  the  life  of  the 
plant  (PFEFFER).  To  the  autonomous  movements  which  occur 
only  once  or  a  few  times  belong  the  hook-like  curvatures  of 
growing  organs,  the  curvatures  of  anthers,  and  the  unfold- 
ing of  floral  envelopes.  The  above-mentioned  circumnuta- 
tion  does  not  belong  here,  since  this  movement  ceases  when 
the  plant  is  placed  upon  the  clinostat  (BARANETZKY).  PFEFFER/ 
however,  considers  it  an  autonomous  movement.  Accord- 
ing to  this  author,  autonomous  nutations  are  perhaps  more 
or  less  present  in  all  organs.  Here  we  must  also  include 


Pflanzenphysiologie,  p.  184. 


280  COMPENDIUM  OF  GENERAL  BOTANY. 

the  movements  of  the  lateral  leaflets  of  Hedysarum  gyrans  as 
well  as  the  movement  known  as  "  rectipetality,"  discovered  by 
VOCHTING.  This  latter  movement  manifests  itself  in  an  effort  of 
geotropically  curved  shoots  to  become  straightened  when  gravity 
is  counteracted  by  means  of  the  clinostat. 

External  causes,  such  as  temperature  and  light,  modify  the 
various  autonomous  movements.1 


D.  IRRITABLE  MOVEMENTS. 

What  has  been  said  in  regard  to  the  effects  of  gravity,  light, 
temperature,  etc.,  is  to  be  applied  herein  so  far  as  movements 
are  concerned.  All  of  the  external  influences  of  the  plant- 
organism  are  stimuli  in  the  wider  sense ;  hence  the  heliotropic, 
geotropic,  and  also  the  nyctitropic  movements  are  irritable  move- 
ments in  the  wider  sense.  We  usually  recognize  irritable  move- 
ments in  a  narrower  sense,  caused  by  mechanical  shock,  or  contact, 
accompanied  by  growth  or  without  growth. 

As  an  example  of  irritable  movement  without  growth  we  will 
discuss  Mimosa  pudica  ;  as  an  example  of  irritable  movement 
with  growth  we  will  discuss  the  behavior  of  tendrils. 

^Mimosa. 

Our  insight  into  the  principles  of  the  mechanics  of  irritable 
and  related  movements  due  to  stimuli  ceases  where  all  deep  and 
far-reaching  investigations  of  life-processes  cease,  namely,  with 
the  question,  Why  does  the  plasm  of  living  cells  become  changed 
in  response  to  certain  stimuli  ?  The  result  of  this  plasmic  be- 
havior— in  this  special  case  the  sudden  passage  of  water  from  the 
cell-lumen  through  the  primordial  utricle  into  the  intercellular 
spaces  and  to  the  exterior — may  then  be  considered  and  explained 
mechanically.  We  owe  our  more  exact  knowledge  in  regard  to 
these  conditions  and  relations  to  BRUCKE  and  PFEFFER.  The 
mechanical  principles  underlying  the  movements  in  Mimosa 
also  apply  to  the  movements  in  the  stamens  of  Cynarece.  In 


1  Incidentally  it  may  be  noted  that  there  is  no  such  contraction  and  relaxation 
in  the  vegetable  tissues  as  is  seen  in  the  muscles  of  animals.  Active  shortenings 
or  contractions  are,  however,  not  wanting  ;  as  has  been  mentioned,  increase  in 
turgor  will  cause  root  parenchyma  cells  to  become  shortened. 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  281 

Mimosa  we  are  concerned  with  curvatures  of  the  leaf-joint 
(motile  organ),  in  the  stamens  of  Oynarece  with  shortening  of  the 
organs.  In  both  cases  there  is  a  sudden  reduction  in  turgor ; 
the  primordial  utricle  suddenly  becomes  very  permeable  to 
water,  allowing  the  water  to  pass  through  its  interstices  and 
finally  also  through  the  cell-wall  into  the  intercellular  spaces. 
Later  this  water  is  taken  up  by  the  cells,  thus  placing  them 
again  in  a  state  of  irritability. 

The  following  statements  are  according  to  the  explanation 
given  by  SACHS,  and  have  special  reference  to  the  petiole  of  the 
Mimosa-leaf. 

1.  The   motile   organ  is   supplied  with  two  tissue-cushions : 
the   loiver   cushion  is   irritable,  the  upper   cushion    causes   the 
movements. 

2.  There  is  a  high  tension  in  the   succulent  parenchyma  of 
the  two  cushions  ;  in  this  condition  they  are  said  to  be  balanced. 
In  the  irritable  state  there  is  also  tension,  but  the  tension  be- 
tween upper  cushion  and  vascular  bundle  is  greater  than  the 
tension  between  lower  cushion  and  vascular  bundle. 

3.  The  decrease  in  volume  in  the  lower  cushion  is  due  to  the 
escape  of  water  from  its  cells,  externally  noticeable  by  a  darker 
coloration.      The   water  escapes  in  part  into  the  intercellular 
spaces  of  the  upper  cushion,  in  part  into  the  tissue  of  the  stem 
and  a  small  portion  into  the  vascular  bundle. 

Behavior  of  Tendrils.     Conduction  of  Stimuli.     The  Function  of 
Irritable  Movements. 

In  tendrils  there  is  an  irritable  movement  induced  by  con- 
tact (not  by  shock)  associated  with  processes  of  growth.  This 
irritability  is  usually  not  general,  but  limited  to  one  side  of  the 
organ.  Groiuth  is  always  reduced  in  the  side  irritated.  As  a  result, 
the  tendril  lying  in  contact  with  some  support,  curves  toward 
that  support  by  a  process  of  circumnutation  ;  this  brings  other 
portions  of  the  tendril  in  contact  with  the  support,  the  stimulus 
is  transmitted  along  the  line  of  contact,  finally  causing  the  entire 
free  portion  of  the  tendril  to  wind  about  the  support  in  the  form 
of  a  spiral.  The  stimulus  is  also  continued  toward  the  basal 
portion  of  the  tendril  (continued  from  the  point  of  contact  above), 
which  cannot  come  in  contact  with  the  support.  The  stimulus 


282  COMPENDIUM  OF  GENERAL  BOTANY. 

(support)  causes  the  formations  of  the  curvatures  or  windings. 
The  support  and  the  tendril  or  climbing  plant  are  drawn  toward 
each  other ;  that  is,  the  tendril  has  a  tendency  to  form  coils 
whose  radii  of  curvature  are  less  than  that  of  the  support,  pro- 
vided the  support  is  not  too  slender  nor  the  tendril  too  thick. 
Besides  these  windings  due  to  contact  there  are  produced  turn- 
ing-points, or  places  where  the  direction  of  the  coil  changes. 
There  may  be  one  or  several  of  these  changes,  and  they  always 
occur  in  the  free  portion  of  the  tendril,  that  is,  in  the  portion 
between  the  support  and  the  stem  of  the  plant;  The  origin  of 
such  coils  is  due  to  a  mechanical  cause,  and  may  be  very  readily 
illustrated  as  follows  :  A  narrow  stretched  strip  of  india-rub- 
ber is  firmly  cemented  along  another  strip  of  rubber  not 
stretched.  Upon  releasing  the  tension  of  the  former  rubber,  it 
contracts  and  forms  the  inside  of  a  spiral,  the  outer  side  of 
which  is  formed  by  the  strip  that  was  not  stretched.  Tendrils 
without  a  support  usually  coil  slowly  in  the  form  of  a  spiral, 
but  ivitliout  the  formation  of  turning-points. 

According  to  DE  VRIES,  the  first  effect  of  the  contact-stimulus 
is  to  increase  the  turgor  of  the  side  not  stimulated.  (For  par- 
ticulars see  the  text-books  of  SACHS  and  PFEFFER.) 

Careful  studies  of  irritability  have  been  made  by  the  DARWINS 
(father  and  son),  later  also  by  WIESNER,  DETLEFSEN,  HABERLANDT, 
and  others.  According  to  Haberlandt,  the  irritable  stimulus  in 
Mimosa  is  propagated  along  a  system  of  special  stimulus-con- 
ducting cells  which  have  highly  permeable  plasmic  membranes 
(pore-membranes)  along  the  transverse  septse.  These  special 
cells  lie  either  within  or  along  the  outside  of  the  leptome-bundle. 
The  permeable  membranes  allow  the  ready  passage  of  water- 
currents,  which  are  supposed  to  be  the  cause  of  the  irritable 
movements. 

The  propagation  of  stimuli  in  tendrils  is  but  little  under- 
stood ;  also  the  propagation  of  stimuli  causing  geotropic  and 
hydrotropic  curvatures.  Opinions  differ  even  in  regard  to  the 
observed  facts  of  the  geotropic  curvatures  of  roots.  I  will 
briefly  state  the  results  of  KRABBE'S  investigations,  which  have 
verified  the  observations  made  by  CISIELSKIS  and  DARWIN. 

The  sensible  or  irritable  portion  of  the  root-tip  is  never  more 
than  2  mm.  long.  The  portion  of  the  root  which  is  really 
capable  of  curving  is  not  wholly  located  in  the  2  mm.  of  the 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE. 

root-tip.  Cutting  off  2  mm.  from  the  root-tip  does  not  prevent 
the  root  from  continuing  its  growth.  Accordingly  Darwin  con- 
cludes that  the  root-tip  rec'eives  a  stimulus  from  the  force  of 
gravity  and  transmits  it  to  the  zone  of  maximum  growth.  Of 
course  it  is  not  implied  that  the  root  possesses  a  "  conscious  " 
power  to  transmit  this  stimulus.  SACHS  maintains,  moreover, 
that  shoots  behave  differently;  they  curve  geotropically  even 
when  the  entire  apex  is  removed.  (According  to  DARWIN,  root- 
tips  undergo  circumnutation  ;  this  is  denied  by  SACHS.) 

In  regard  to  the  utility  of  irritable  movements  due  to  shock 
and  contact  we  will  state  the  following :  In  the  case  of  tendrils 
this  utility  is  very  evident,  for  by  such  irritable  movements 
they  are  enabled  to  function  as  organs  of  adhesion  and  support. 
The  irritable  movements  of  the  stamens  of  Cynarece  are  de- 
scribed and  explained  as  follows.  A  visiting  insect  causes  the 
stimulus  by  coming  in  contact  with  the  anther,  which  thereby 
suddenly  contracts  the  anther-tube,  while  the  hair-like  bristles 
of  the  style  which  is  not  irritable  "  brushes  "  out  some  of  the 
pollen,  which  is  carried  away  by  the  insect  to  fertilize  another 
plan-t.  In  regard  to  Mimosa,  SACHS  made  the  observation  that 
this  plant  is  able  to  withstand  hail  much  better  than  more  robust 
plants,  because  the  very  first  contact  suffices  to  place  it  in  the 
irritated  position ;  that  is,  the  leaflets  become  folded  and  the 
petiole  sinks.  PFEFFER  supposes  that  such  movements  also 
serve  as  a  protection  by  frightening  away  animals.  Among 
"  insectivorous  "  plants  the  irritable  organs  serve  to  catch  in- 
sects, as  has  been  explained  in  the  case  of  Drosera. 

E.  THE  PHYSIOLOGY  OF  TWINING. 

One  of  the  most  complicated  phenomena  in  the  plant-creation 
is  the  twining  of  plants.  It  is  not  an  irritable  movement  in  the 
narrower  sense,  produced  by  shock  and  contact.  Here  we  find 
combined  with  circumnutation  the  effect  of  negative  geotropism 
and  the  influence  of  apparent  and  real  torsion. 

It  is  well  known  that  the  stem  of  a  climbing  plant  (as  hops, 
beans,  Calystegia,  Jpomcea,  etc.)  winds  about  a  support  in  the  form 
of  a  spiral.  The  mechanics  of  this  process  is  essentially  dif- 
ferent from  that  of  the  winding  of  tendrils.  To  understand  it 
well  it  is  necessary  for  the  investigator  to  have  special  prepara- 


284 


COMPENDIUM  OF  GENERAL  BOTANY. 


tion  in  mechanics  and  mathematics.     The  study  of  this  problem 
was  begun  by  VON  MOHL  and  PALM,  and  continued  by  CHARLES 
DARWIN  and  H.  DE  VRIES.     Great  advances  in  this  study  have 
recently  been   made    by   the    investigations   of    SCHWENDENER, 
BARANETZKY,  and  AMBRONN.     The  following  explanation  is  based 
upon  the  results  of  AMBRONN'S  and  SCHWENDENER'S  investigations. 
The  active  factors  in  twining  are  (1)  circumnutation  of  the 
growing  stem-apex  and  the  resistance  of  the  support  ;  (2)  nega- 
tive geotropism.     Both  factors  aid  each  other  in  their  effects. 
Circumnutation  makes  seizure  of  or  contact  with  the  support 
possible  ;  subsequently  it  is  necessary  that  the  contact-stimulus 
should  continue  upward  and  that  the  curvature  should  be  con- 
tinuous for  a  time  at  least.     The  advancing  of  the  contact-point 
is  induced  by  the  return  pressure  of  the  sup- 
port.    The   support  exerts  a  radial  pressure 
outward  against  the  point  of  contact  behind 
a  (Fig.  171),  which  necessarily  increases  and 
extends  the  contact  area  at  ft.     Antidromic 
torsions  prevent  a  stem-portion  as  at  y,  which 
must  become  somewhat  elongated  on  the  side 
facing   the    support  due    to   the  pressure   of 
the  support,  from  elongating  equally  on  the 
outer  side  when  it  comes  into  the  position  /?. 
Negative  geotropism  causes  the  horizontally 
or  diagonally  placed   apical    stem-portion  to 
curve  upward  and  again  brings  it  in  contact 
with  the  support  at  some  point  higher  up,  when  the  effects  of 
the  pressure  will  again  come  into  play,  as  has  just  been  ex- 
plained.    Negative  geotropism  also   assists  in  another  way  in 
forming  permanent  spirals.     It  causes  curvatures  by  the  more 
active  growth  of  a  continuous  tissue-portion  which  describes  a 
homodromic  spiral  line  around  the  stem. 

We  have  yet  to  mention  the  influence  of  apparent  1  and  real 
torsion  in  the  process  of  twining.  According  to  Ambronn  and 
Schwendener,  apparent  torsion  causes  spiral  curvatures,  which 


FIG.  171. 


1  Au  apparent  torsion  may  be  represented  by  a  cylindrical  staff  cut  into  many 
sections,  fastened  together  by  spirally-arranged  hinge-  joints,  which  are  wound 
about  some  support.  In  the  case  of  twining  true  torsions  are  caused  by  the  lat- 
eral pressure  of  the  support  acting  upon  a  diagonal  portion  of  the  stem.  (See 
Fig.  171.) 


THE  GENERAL   CHEMISTRY  AND  PHYSICS  OF  PLANT-LIFE.  285 

hasten  or  favor  the  twining  about  the  support.  The  amount  of 
true  antidromic  torsion  influences  in  a  high  degree  the  mobility 
of  the  iuternodes,  so  that  the  amplitude  of  the  movements  of 
nutation  decreases  with  the  increase  of  antidromic  torsion. 
(Within  certain  limits  the  amount  of  true  torsion  increases  as 
the  thickness  of  the  support  increases.  Apparent  torsion  in- 
creases with  the  closeness  of  the  spirals.) 

SCHWENDENER  has  demonstrated  that  by  eliminating  the 
weight  of  the  overhanging  stem-apex  twining  is  not  in  any  way 
disturbed,  which  proves  that  the  weight  of  the  plant  is  not  an 
essential  factor  in  the  process  of  twining. 


PAET  VI. 

CLASSIFICATION  OF  PLANTS. 
TAXONOMY. 


A  system  of  classification  is  said  to  be  artificial  when  it  is 
based  upon  limited  but  constant  characters.  A  system  is  said 
to  be  natural  when  it  is  based  upon  all  the  characters  of  the 
organism.  Usually,  however,  the  idea  of  "  natural  descent "  is 
associated  with  a  natural  system.  It  is  supposed  that  descent 
is  the  cause  of  the  resemblance  or  similarity  of  the  plants  or 
other  organisms.  It  is  generally  admitted  that  the  natural 
system  which  is  to  be  the  expression  of  natural  origin  and 
descent  is  being  gradually  discovered,  hence  does  not  yet 
actually  exist.  It  is  customary  at  present  to  consider  the 
natural  system1  as  directly  opposed  to  the  system  of  LINNE.' 
Nevertheless  the  system  of  Linne  as  well  as  the  various  natural 
systems  are  at  the  same  time  natural  and  artificial. 

Many  of  the  plant-families  of  the  so-called  natural  systems 
coincide  more  or  less  with  the  classes  or  orders  of  Linne's  sys- 
tem.3 The  following  table  will  illustrate  this  more  clearly. 

The  families  given  at  the  right  harmonize  with  the  following 
classes  and  orders  of  Linne : 


1  A.  L.  DE  JUSSIEU  is  usually  credited  with  having   introduced  the  natural 
system  of  plants.— TRANS. 

2  See  p.  288  for  Linne's  Classification. 

3  Acherson,  Flora  der  Provinz  Brandenburg. 


CLASSIFICATION  OF  PLANTS.     TAXONOMY.  287 

III.  Class Graminese. 

V.  "      1.  Order , Primulaceae. 

V.  "            "       Boraginaceae. 

V.  "            "       Solanacese. 

Y.  "      1.  and  2.  Order Gentianaceae. 

V.  "      2.  Order Umbelliferse. 

V.  "            "       ChenopodiaceaB. 

VI.  "       Liliiflorse  (in  part). 

XII.  " Rosaceae. 

XIII.  "      1.  Order „ Papaveraceae. 

XIII.  "      2.  and  3.  Order Ranunculaceae. 

XIV.  "      1.  Order Labiatse. 

.      XV.      "      Cruciferte. 

XVI.  and  XVII.  Class Papilionaceae. 

XIX.  Class. . » Compositse. 

XX.      "     Orchidaceae. 

XXI.      "     Cupuliferse. 

XXI.      "     Conifers. 

That  Linne's  system  of  phanerogams  is  artificial  is  evident 
from  the  fact  that  it  includes  the  Coniferm  and  Oupuliferce  in  one 
and  the  same  class.  He  has  also  combined  the  Umbelliferce, 
Itoraginacece,  Solanacece,  etc. 

Nevertheless  the  system  of  Linne  is  in  part  natural  and  in 
part  artificial.  This  is  true  of  all  phanerogamic  systems,  hence 
also  of  every  system  which  is  said  to  be  natural  as  opposed  to 
the  system  of  Linne.  The  impartial  scientist 1  may  well  ques- 
tion the  value  of  the  much-praised  naturalness  of  the  natural 
systems.  I  say  natural  systems,  because  there  are  a  large  num- 
ber of  them.  It  is  wholly  out  of  the  question  at  the  present 
time  to  consider  all  of  the  characteristics  in  the  arrangement  of 
plants.  The  essentials  of  these  natural  systems  are  based  upon 
the  characters  of  the  flower  and  the  fruit. 

The  value  of  anatomical  characters  has  long  been  proven. 
These  characters  have,  however,  only  been  applied  within 
narrow  limits.  It  has  even  been  supposed  that  comparative 
anatomy  would  sooner  or  later  come  in  serious  conflict  with  the 
present  natural  systems.  I  do  not  believe,  that  comparative 


1  Compare  Schwendener's  Rectoratsrede,  Berlin,  1887. 


288 


COMPENDIUM  OF  GENERAL  BOTANY. 


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CLASSIFICATION  OF  PLANTS.     TAXONOMY.  289 

anatomy  will  ever  aid  in  establishing  a  natural  system  of  the 
various  dicotyledonous  groups,  based  upon  descent,  because 
such  a  system  is  not  possible.  We  may,  no  doubt,  succeed  in 
arranging  certain  groups  upon  definite  anatomical  characters. 
These  characters  are,  however,  useless  when  applied  to  other 
groups.  Again,  it  will  be  found  that  the  selection  of  other  ana- 
tomical characters  will  lead  to  a  different  arrangement.  The 
reason  that  we  cannot  find  a  system  which  would  also  represent 
a  phylogenetic  tree  lies  in  the  absence  of  a  natural  descent,  and 
not  in  the  lost  or  hidden  branches  of  this  tree.  The  bond  which 
unites  the  organisms  of  a  kingdom  is  a  spiritual  one,  it  is  the 
uniform  Creative  Idea.  A  phylogenetic  relationship,  if  it  exists 
at  all,  is  very  limited. 

In  conclusion  I  will  give  the  plant-system  of  EiCHLEB.1 

A.  Cryptogamae. 

I.  DIVISION  :  THALLOPHY™. 
/.   Class :  Algce. 

I.  Group :  CyanophyceaB. 
II.        "        Diatomese. 
III.         "         Chlorophycese. 

1.   Series  :   Conjugate ;   2.   series :    Zoospo- 
rese ;  3.  series  :  Characese. 
IV.  Group  :  Phaeophycese. 
Y.         "        Ehodophycese. 
//.   Class  :  Fungi. 

I.  Group  :  Schizomycetes. 
II.         "        Eumycetes. 

1.  Series  :  Phycomycetes ;  2.  series :  Ustila- 
ginese  ;  3.  series  :  ^Ecidiomycetes  ;  4.  series : 
Ascomycetes  ;  5.  series  :  Basidiomycetes. 
III.  Group  :  Lichenes. 
II.  DIVISION:  BKYOPHYTA. 

I.  Group :  Hepaticaa. 
II.        "        Musci. 
III.  DIVISION:  PTEKIDOPHYTA. 

/.    Class :  Equisetince. 
11.        "       Lycopodince. 
III.        "       Filicince. 


Syllabus,  1886. 


290  COMPENDIUM  OF  GENERAL  BOTANY. 

B.  Phanerogam*. 

I.  DIVISION  :  GYMNOSPERM^E. 
II.          "         ANGIOSPERM^;. 
/.  Class:  Monocotylece. 

1.  Series  :    Liliiflorae  ;    2.  series  :    Enantio- 
blastse  ;  3.  series  :   Spadiciflorse  ;  4.  series  : 
Glumiflorae ;  5.  series:  Scitarnineae;  6.  series: 
Gynandrae  ;  7.  series  :  Helobiae. 
II.  Class:  Dicotylece. 

I.  Subclass  :  Choripetalae. 

1.  Series  :  Amentaceae  ;  2.  series  :  Urticinae ; 
3.  series :  Polygoninae ;  4.  series :  Centro 
spermae  ;  5.  series  :  Polycarpicae  ;  6.  series  : 
B/hoeadinae  ;  7.  series  :  Cistiflorae  ;  8.  series  : 
Columniferae ;  9.  series  :  Gruinales  ;  10.  se- 
ries :  Terebinthinae ;  11.  series  :  ^Esculinae  ; 
12.  series:  Frangulinae ;  13.  series:  Tricoc- 
cae  ;  14.  series  :  Umbelliflorae  ;  15.  series  : 
Saxifraginse  ;  16.  series  :  Opuntinse ;  17.  se- 
ries :  Passiflorinse  ;  18.  series  :  Myrtiflorse  ; 
19.  series  :  Tliymelinae  ;  20.  series  :  Eosi- 
florse  ;  21.  series  :  Leguminosae  ;  appendix  : 
Hysterophyta. 
II.  Subclass  :  Sympetalse. 

1.  Series  :  Bicornes  ;  2.  series  :  Primulinse  ; 
3.  series  :  Diospyrinae  ;  4.  series :  Contorts ; 
5.  series :  Tubiflorse ;  6.  series :  Labiati- 
floraa  ;  7.  series  :  Campanulinse  ;  8.  series  : 
Kubiinae ;  9.  series  :  Aggregate. 

ENGLEE1  divides  the  monocotyledons  into  ten  series.  The 
Palmce,  Pandanales,  Spathiflorce,  and  Synanthce  are  treated  as 
special  series.  He  also  subdivides  the  Choripetalce  more  than 
does  Eichler.  Both  authors  almost  agree  in  the  arrangement 
of  the  Sympetalce.  Engler  treats  the  Plantaginales  as  a  distinct 
series. 

Finally,  we  will  refer  to  Nageli's  system  of  classification. 
This  investigator  was  especially  anxious  to  establish  a  natural 
system,  but  he  could  not  decide  whether  the  monocotyledons  or 


1  Guide  to  the  Royal  Botanical  Garden  of  the  University  at  Breslau,  1886. 


CLASSIFICATION  OF  PLANTS.     TAXONOMY.  291 

the  dicotyledons  constituted  the  most  highly  organized  group 
of  plants.  He  was,  however,  inclined  to  consider  the  monocoty- 
ledons as  the  higher  group.  This  author  maintains  that  certain 
families  have  become  extinct,  and  therefore  the  phylogenetic  con- 
nection is  no  longer  directly  visible.  Should  this  connection  be 
visible  we  would  find,  according  to  Nageli,  the  lower  uniting 
branches  of  the  phylogenetic  tree  ;  these  lower  branches  have 
become  extinct.  All  this  assumption  is  pure  speculation.  It  is 
not  probable  that  a  system  of  natural  descent  will  ever  be  estab- 
lished. Since  Nageli  desires  to  establish  such  a  system,  he  must 
assume  the  original  existence  of  such  extinct  plant-groups,  of 
which  even  palaeontology  reveals  no  record. 

Natural  in  the  sense  of  according  to  nature  (not  in  the  sense 
of  according  to  a  natural  descent)  is  that  arrangement  of  plants 
which  proceeds  from  simpler  forms  to  those  more  complicated. 
We  may  also  say  that  the  arrangement  of  series  from  "  lower  "  to 
"higher"  is  natural;  but  not  from  "imperfect"  to  "perfect." 
(It  would  be  wrong  and  meaningless  to  say  an  alga  is  imper- 
fect because  it  lacks  vascular  bundles  ;  the  algse  do  not  require 
such  organs.)  The  arrangement  of  plants  into  cellular  plants 
and  vascular  plants,  into  cryptogams  and  phanerogams,  into 
thallophytes  and  cormophytes  (plants  with  stems  and  leaves), 
seems  according  to  nature.  Not  any  observed  facts  of  a  natural 
descent,  but  our  reasoning  faculty,  leads  us  to  make  such  classi- 
fications. It  is  a  spiritual  bond  which  unites  all  organisms. 
This  bond  is  the  Idea  of  the  Creator. 


GENERAL  INDEX. 


Abnormal,  s.tem  and  root,  94 

Absorption-cells,  144 

Absorption  of  assimilated  substances, 

141 

Acheuium,  232 
Achromatin,  12 
Acropetal  order  of  development,  69, 

170,  172 

Actinic  rays,  130 
Actinomorphic,  219 
Active  growth,  261 
Acyclic,  218 
Adaptation,  243,  246 
Adhesion,  61 

Adventitious  formations,  166 
^Ecidium,  197 
Aeration,  132 
Aerial  roots,  140 
^Estivation,  166 
JSthusa,  221 
Agave,  158 
Age  of  plants,  250 
Aggregate  fruits,  231 
Albumen,  151 

Albumen-conducting  elements,  72,  O'x 
Albuminoids,  4,  5,  21,  99,  251 
Aleurou,  21 
Algge,  192 
Alkaloids,  256 
Aloe.  54,  150 

Alternation  of  generation,  186,  200 
Amides,  99 
Ammonia,  255 
Amphitropous,  229 
Amylodextrin,  20 
Amylum,  17,  131 
Anatropous,  228 
Andrcecium,  216,  222 
Androspore,  193 
Anemophilous,  239 
Angiosperms,  210 
Animals,  148 
Annual  plants,  158 
Annual  ring,  90 
Annular  vessels,  35 
Annulus,  226 
Anther,  223 
Anther-case,  227 
Antheridium,  189 
Anthers,  223 
Antipodal  cells,  209,  229 
Antipodes,  209 


Ants,  148 

Apetalous,  215 

Apical  cell,  118,  169 

Apical  growth,  11,  46,  48 

Apogamy,  243 

Apotropous,  229 

Apple,  233 

Apposition,  17,  27 

Aqueous  tissue,  55,  150 

Archegoniuni,  189 

Arillus,  233 

Aroids,  140 

Ascent  of  sap,  108 

Ascomycetes,  43,  196 

Ascospore,  43 

Asexual  generation,  185 

Asexual  propagation,  186 

Asexual  reproduction,  186 

Ash,  252 

Asparagin,  24 

Assimilation,  122 

Atavism,  242 

Atropous,  228 

Autonomous  movements,  279 

Autumnal  wood,  89 

Auxanometer,  269 

Axil,  166 

Axillary  placentation,  228 

Axillary  shoots,  118,  166 

Azygomorphic,  219 

Bacteria,  129 
Bacteroids,  16 
Bark,  56 
Basidia,  196 

Basidiomycetes,  44,  196 
Basidiospore,  196 
Basidium,  196 
Bast,  72 
Bast- cell,  72 
Bast-rib,  79 
Bast-ring,  spiral,  93 
Bast-tissue,  72 
Berry,  233 
Biennial  plants,  158 
Bifacial,  127 
Bilateral  structure,  166 
Biogenesis,  162 
Bisexual,  187 
Bleeding,  107 
Bordered  pits,  38 
Bostrychoid,  183 


293 


294 


GENERAL  INDEX. 


Bostryx,  183 
Bract,  163,  181 
Branching,  179,  183 
Bud,  165 
Budding,  44 
Bulb,  157 

Calcium,  253 
Calcium  oxalate,  22 
Callus,  92 
Calyptra,  202 
Calyptrogeu,  117 
Calyx,  214 

Cambiform  tissue,  75 
Cambium,  73,  81,  87 
Cambium-cell,  87 
Campylotropous,  229 
Canal  of  the  style,  212 
Capillary  attraction,  104 
Capillitium,  196 
Capsule,  232 
Carbohydrates,  101 
Carbon,  122 
Carbon  dioxide,  122 
Carpel,  212,232 
Carpellary  leaf,  212 
Catabolic  processes,  258 
Cataphyllary  leaves,  162 
Caulerpa,  10 
Caulome,  157 
Cecropia,  148 
Cell,  4 

Cell-body,  46 
Cell-contents,  10 
Cell-division,  12 
Cell-formation,  42 
Cell-forms,  70,  75 
Cell -growth,  259 
Cell-membrane,  4,  5,  7 
Cell-sap,  24 
Cell-surface,  46 
Cell-threads.  46 
Cellulose,  30 
Cell-wall,  25,  260 
Cell-wall  formation,  259 
Central  passage,  135 
Centric  structure,  127 
Chalaza,  229 
Characeae,  193 
Chasmogamous,  239 
Chemical  rays,  130 
Chemism,  252 
Chlorophyll,  14,  128 
Chlorophyll-bodies,  14 
Chlorophyll-granules,  13 
Chlorophyll  movement,  128 
Chlorophyll-spectrum,  129 
Chloroplastids,  14 
Chromatin,  12 
Chromatophore,  6 
Chromoplastids,  13 
Cicinus,  182 
Cilia,  16 
Circulation  of  plasm,  276 


|    Circumnutation,  277 
Cleistogamy,  239 
Climbing  plants,  283 
Climbing  stems,  283 
Cliuostat,  264 
Closed  bundles,  82 
Collecting  cells,  126 
Color  of  leaves  in  autumn,  15,  132 
Columella,  202 
Competition,  248 
Conducting  tissue,  74,  99 
Conferva,  193 
Couidia,  194 
Coniferse,  15 
Conjugation,  188,  193 
Connective,  224 
Constancy,  243,  244 
Cork,  56 

Cork-cambium,  56 
Corolla,  214 
Correlation,  167 
Cotyledon,  161 
Cremocarp,  232 
Cross-pollination,  238 
Cryptogams,  188 
Crystalloids,  21 
Crystals,  22 
Culm,  158 
Cupula,  231 
Curvatures,  263 
Cuticle,  54,  135 
Cuticularization,  30 
Curvatures,  263 
Cyclic,  217      . 
Cyme,  182 
Cynarece,  280 
Cystolith,  32 
Cytoplasm,  6 

Dedoublement,  218 
Dehiscence,  231 
Derived  hybrids,  242 
Dermatogeu,  49 
Dermocalyptrogen,  117 
Descent,  natural,  244 
Desmids,  40 
Diastase,  19,  237 
Diatomacese,  192 
Dichasium,  183 
Dichogamy,  239 
Diclinous,  187,  239 
Dicotyledons,  80 
Dioecie,  187 
Diosmose,  101 
Direct  cell  formation,  43 
Divergence,  172,  174 
Dorsi  ventral,  166,  170 
Doubling  of  flowers,  218 
Drosera,  149 
Drupe,  232 
Dry  substance,  252 
Dynamical  cells,  278 

Egg-cell,  204 


GENERAL  INDEX. 


295 


Egg-cell  apparatus,  213 
Elasticity,  64 
Elective  choice,  8 
Electricity,  276 
Embryo,  230 
Embryo-sac,  227 
Embryology,  2 
Emergences,  156 
Endocarp,  232 
Endoderrn,  112,  140 
Endogenous,  169 
Eudophyte,  144 
Eudosmose,  1U1 
Endosperm,  142,  230 
Eudospore,  194 
Eudothecium,  225 
Energy  of  growth,  261 
Entomophilous,  215,  239 
Environment,  243 
Epicarp,  232 
Epidermal  tissue,  53 
Epidermis,  53 
Epigynous,  216 
Epiiiasty,  261 
Epiphyte,  140,  144 
Epithem,  108 
Epitropous,  229 
Equisetuin,  79 
Etiolation,  272 
Evaporation,  53 
Excretion,  152 
Exogeus,  169 
Extrorse,  224 
Eye-spot,  16 

Falling  of  leaves,  58 

Fascicular  cambium,  74 

Faseicular  tissue,  74 

Female  prothallium,  202 

Fermentation,  257 

Ferments,  19   149,  237 

Fern-prothallium,  203 

Ferns,  201 

Fertility,  241 

Fertilization,  214,  238 

Filament,  223 

Floral  diagrams,  218 

Floral  leaves,  163 

Florideae,  13 

Flower,  213 

Fluorescence  of  chlorophyll,  130 

Foliage-leaves,  162 

Follicle,  232 

Food-substances,  122,  141,  258 

Foot,  208 

Formative  tissue,  87,  169 

Free  cell-formation,  42,  43 

Freezing,  270 

Fruit,  231 

Fucoideae,  194 

Fundamental  tissue,  81 

Functions,  49,  59 

Fungi,   194 

Fuuiculus,  213,  228 


Galvanotropism,  276 
Gametes,  191 
Gasteromycetes,  196 
Genetic  spiral,  171 
Genus,  245 
Genus-hybrid,  241 
Geotortism,  265 
Geotropism,  263,  275 
Germination,  237 
Germs,  185 
Girdling,  100 
Glands,  153 
Glandular  hairs,  153 
Gleba,  196 

Gliding  growth,  48,  88 
Globoids,  22 
Glceocapsa,  27 
Glucose,  24 
Glume,  163 
Gonidia,  146 

Grand  period  of  growth,  269 
Gravity,  influence  of,  275 
Ground-spiral,  171 
Growth,  50 

active,  261 

gliding,  48 

passive,  261 

periodicity  of,  269 
Guard-cells,  135 
Gum,  92 

Gynmosperms,  80,  210 
Gyncecium,  216,  222,  227 

apocarpous,  228 

mouomerous,  228 

polycarpous,  228 

polymerous,  228 

syucarpous,  228 

Hadrome,  75 
Hair-cells,  61,  156 
Haustoria,  144 
Heart- wood,  92 
Heat,  action  of,  269 

production  of,  268 

radiation  of,  276 
Helicoid  cyme,  183 
Heliotortism,  265 
Heliotropism,  263,  274 
Hemicyclic,  218 
Hermaphrodite,  187 
Heredity,  243 
Hetercecie,  197 
Heterosporous,  204 
Heterostyly,  240 
Hiltim,  18,  229 
Hyaloplasm,  6 
Hybrid,  241 
Hybridization,  241 
Hydro-diffusion,  101 
Hydrophilous,  239 
llyd  rot  ropism,  263,  276 
Hygroscopic  movements,  278 
Hyphal  tissue,  196 
Hypocotyledonary  axis  or  stem,  158 


296 


GENERAL  INDEX. 


Hypogynous,  216 
Hypouasty,  261 
Hypsophyllary  leaves,  162 

Ice,  formation  of,  270 
Idealism,  175 
Idioplasm,  13,  245,  250 
Imbibition,  20,  103 
Inbreeding,  240 
Indusium,  207 
Inferior  ovary,  216 
Inflorescence,  181 
Inorganic  cells,  259 
Insectivorous  plants,  148 
Insertion  of  leaves,  171 
Integument,  53 
Intercalary  growth,  119 
Intercellular  cement,  41 
Intercellular  spaces,  132 
Intel-nodes,  165 
Inline,  227 
Introrse,  224 

Intussusception,  17,  18,  27 
Inulin,  24 
Involucre,  221 
Irritability,  280 
Isolateral,  126 
Isotouic  coefficients,  9 

Jamiu-chains,  107,  111 
Karyokiuesis,  12 

Labiatse,  220,  222 

Lamina  of  leaf,  159 

Land-plants,  133 

Lateral  budding,  166, 168 

Lateral  organs,  168 

Lateral  shoots,  183 

Laticiferous  tissue,  76 

Leaf,  159 

Leaf-bearing  axis,  165 

Leaf -base,  159 

Leaf -blade,  160 

Leaf-coloration,  15,  163 

Leaf,  falling  of,  58,  132 

Leaf-forms,  164 

Leaf -margin,  160 

Leaf -modification,  163 

Leaf-sheath,  159 

Leaf-tendrils,  167 

Leaf-trace,  59,  83 

Leaflet,  161 

Legume,  232 

Leguminosae,  20 

Lenticels,  138 

Leucoplastids,  13,  14 

Libriform,  75 

Lichens,  48,  127,  145,  199 

Life-period,  250 

Light,  123 

action  of,  123,  270 
production  of,  270 

Liguification,  31 

Ligules,  160 


Linear  thickenings,  34 
Locomtor  movements,  278 
Loculicidal  dehiscence,  23& 
Lodiculse,  214 
Loment,  232 
Lysigeuous,  154 

Macrospore,  204 
Male  prothallium,  193,  205 
Mangrove-tree,  159 
Margo,  39 
Marsh-plants,  133 
Mechanical  cells,  70 
Mechanical  system,  63 
Mechanical  theory,  175 
Mechanics  of  growth,  258 
Mechanics  of  plasm,  258 
Median  plane,  219 
Median  zygouiorphic,  219 
Medullary  ray,  73 
Meristem,  115,  169 
Mesocarp,  232 
Metabolic  processes,  258 
Metamorphosis,  167 
Micellae,  30,  266 
Micellar  theory,  266 
Micropyle,  211 
Microspore,  204 
Middle  lamella,  41 
Milk-tissue,  76 
Mimosa,  280 
Modulus  of  elasticity,  65 
Moisture,  276 
Molecular  structure,  266 
Molecular  tension,  267 
Monocarpous,  158 
Monocotyledons,  80 
Monoecious,  187 
Monomerous,  228 
Mouopodium,  179 
Morphology,  1,  2 
Mosses,  78 
Movements,  277 
Mycorhiza,  147 
Myrmecophilous,  148 

Natural  descent,  244 
Natural  selection,  246 
Natural  system,  286 
Natural  varieties,  248 
Neck,  189 
Nectaries,  215,  222 
Negative  geotropism,  275 
Negative  heliotropism,  271 
Neutral  flower,  164 
Node,  165 
Normal  series,  174 
Nucellus,  211 
Nuclear  division,  12 
Nuclei  n,  11 
Nucleoli,  11 
Nucleus,  10 
Nut,  232 
Nutation,  277 


GENERAL  INDEX. 


297 


Nyctitropic  curvatures,  264 
movements,  273 

Oedogonium,  193 
Oil-glands,  154 
Oogonium,  189 
Oomycetes.  194 
Oospore,  188 
Open  bundles,  82 
Organic  acids,  140 
Organs  of  plants,  155,  244 
Origin  of  species,  244 
Ortiiostichy,  179 
Ortbotropic,  275 
Ortbotropous,  228 
Osmosis,  106 
Ovary,  212,  228 
Ovule,  227 
Oxygen,  253 

Palisade-cells,  123 
Panicle,  182 
Parasites,  143 
Parastichy,  178 
Parenchyma,  41 
Parietal  placentation,  228 
Parmelia,  146 
Passive  growth,  261 
Peduncle,  163 
Peloric  flowers,  219 
Perennial  plants,  158 
Perianth,  215 
Periblem,  49 
Pericambium,  60 
Pericarp,  232 
Periuiuin,  196 
Perigynous,  217 
Perisperm,  230 
Peristome,  202 
Permanence,  244 
Petiole,  160 
Pbelloderm,  57 
Phellogen,  56 
Phloem,  75 
Pbloim-bundle,  75 
Pbospborus,  254 
Pbototonous,  273 
Pbylloclades,  160 
Pbyllodes,  160 
Pbyllome,  157,  159 
Pbyllotaxy,  171,  175 
Pbylogeny,  245 
Physiology,  1,  2,  252,  258 
Pinnae,  161 
Pinnulse,  161 
Pitted  vessels,  35 
Placenta,  212 
Plagiotropic,  275 
Plane  of  symmetry,  219 
Plant-diseases,  197 
Plasm,  4 

Plasmic  movement,  277 
Plasmic  utricle, 4-6 
Plasmolysis,  7-9 


Pleon,  267 
Plerome,  49 
Pleurotropous,  229 
Polioplasm,  6 
Pollen-grain,  211,  223 
Pollen -sac,  223 
Pollen-tube,  204,  212 
Pollination,  238 
Pollinium,  227 
Polycarpous,  158 
Polymerous,  228 
Pore,  36 
Pore-canal,  37 
Pore-membrane,  38 
Porous  thickenings,  34, 36 
Potassium   253 
Primary  cortex,  91 
Primary  membrane,  41 
Primary  vessels,  35 
Primordia,  219 
Primordial  utricle,  5, 7 
Proniyceliurn,  198 
Pro-nucleus,  241 
Prosencbyma,  41 
Protaudry,  239 
Proteids,  99 
Protballium,  202 
Protococcus,  193 
Protogynous,  239 
Proton  ema,  194 
Protoplasm,  4 
Pseudaxis,  180 
Pseudo-parenchyma,  199 
Pucciuia,  197 
Pyreuoids,  15 

Raceme,  182 

Racemose  infloresence,  182 

Radial  structure,  166 

Rank,  183 

Raphe,  229 

Receptacle,  216,  231 

Reciprocal  hydrids,  241 

Rectipetality,  280 

Reproduction,  185 

Reserve  materials,  150 

Reservoirs  for  reserve  materials,  142 

Resin,  152,  256 

Resin-ducts,  153 

Respiration,  256 

Rest  period,  237 

Resupiuatiou,  220 

Retardation  of  growth  by  light,  273 

Reversion,  242 

Rbeotropism,  276 

Rhexigenous,  154 

Rbizoids,  140 

Rhizome,  157 

Root,  157 

Root- cup,  47,  116 

Root- hairs,  139 

Root- pressure,  107 

Roots,  139 

Root-sheath,  112 


298 


GENERAL  INDEX, 


Root-structure,  46,  95 
Root-tubercles,  16,  148,  253 
Rosette,  166 
Runners,  158 

Sacharomyces,  44 
Sap,  of  cells,  24 
Saprophytes,  143 
Scalarif  orin  vessels,  35 
Scar-tissue,  58 
Sclereuchyma,  41,  232 
Scission- layer,  58 
Scission-tissue,  235 
Sclerotium,  199 
Scorpioid  cyme,  183 
Scutellum,  142 
Secondary  bundles,  35 

roots,  169 

spirals,  174 
Secretion,  152 
Sectio  aurea,  175 
Seed,  142,  231 

Segmentation  of  the  apical  cell, 
Selaginella,  204 
Selection,  248,  257 
Self-fertilization,  239 
Self-pollination,  238 
Sepals,  215 

Septicidal  dehiscence,  232 
Septifragal  dehiscence,  233 
Sexual  affinity,  241 

generation,  203 

reproduction,  185 
Sheath,  of  leaf,  159 
Shoot,  165,  183,  184 
Sieve- cells,  74 
Sieve- plates,  74 
Sieve -pores,  74 
Sieve- tubes,  74 
Silique,  232 
Sinistrorse,  174 
Skeleton-cells,  87 
Sleep  of  plants,  273 
Soredia,  199 
Special  creation,  244 
Species,  241,  244 
Species,  origin  of,  244 
Species,  hybrid,  241 
Spectrum  of  chlorophyll,  129 
Spermatia,  198 
Spermatozoid,  189 
Spermogonia,  198 
Sphacelium,  199 
Sphaero-crystals,  24 
Spike,  182 
Spikelet,  183 
Spiral  arrangement,  171 
Spiral  lines,  171 
Spiral  theory,  171 
Spiral  vessels,  35 
Splint-wood,  92 
Spongy  parenchyma,  126 
Spontaneous  generation,  245 
Sporangia,  207 


Sporangiophores,  195 

Spore,  188 

Sporidia,  198 

Sporocarp,  196 

Sporogouiurn,  202,  206 

Stamen,  223 

Staminal  leaves,  165 

Stamiuodia,  218 

Starch,  17,  151 

Starch- forming  corpuscles,  13 

Starch -grains,  17 

Stem,  80,  157 

Stern  structure,  46,  80 

Stereids,  41 

Stereome,  41 

Stigma,  212 

Stimuli,  conduction  of,  281 

Stipule,  159 

Stomata,  135 

Stone-fruit,  232 

Storage-tissue,  151 

Stratification,  17,  21,  26 

Striation  of  cell-wall,  26 

Strawberry,  231 

Struggle  for  existence,  246 

Stylar  duct,  212 

Style,  212 

Suberiu,  31 

Subsidiary  cells,  137 

Sulphur,  254 

Summer-spores,  197 

Suppression,  218 

Surface-growth,  27 

Suspeusor,  211 

Swarm-spore,  195 

Swelling.  20 

Symbiosis,  145 

Symmetry,  219 

Sympetalous,  61 

Sympodium,  180 

Syncarpous,  228 

Synergitlae,  213,  229 

System,  natural,  286 

Systems  of  organs,  155, 179 

Tannin,  6,  153,  256 
Tapetal  cells,  227 
Taxonomy,  188,  286 
Tegmen,  235 
Tegument,  53 
Teleutospore,  197 
Temperature,  268 
Tendrils,  281 
Tension,  64,  262 
Tentacle,  149 
Testa,  235 
Tetrad,  227 
Tetrarch,  97 
Tetraspore,  194 
Tlmllome,  156,  162 
Theory  of  descent,  244 
Thermotropism,  276 
Thickenings,  33 
Tilletia,  198 


GENERAL   INDEX. 


299 


Tissues,  45 
Tissue-tension,  262 
Tissue-trichomes,  156 
Torsion,  264,  277 
Torus,  88,  216,  228 
Tracheids,  72 
Trama,  196 

Transpiration,  108,  126 
Transition,  164 
Transition -zone,  98 
Triaxial,  183 
Trichogyne,  194 
Tricuomes,  61,  63,  165 
Tuber,  158 
Tuberidia,  158 
Turgor,  7,  259 
Twining,  283 
Tyloses,  58 

Umbel,  182 
Uniaxial,  183 
Uredospores,  198 
Ustilagineal,  196 

Vacuole,  4 
Variation,  243 
Variation  of  hydrids,  243 
Varieties,  243 
Variety-hybrid,  241 
Vascular  bundles,  81,  83 
Vascular  cryptogams,  78 


Vaucheria,  193 
Vegetative  cells,  205 
Vegetative  rest,  237,  250 
Vegetative  period,  250 
Velamen,  140 
Venation,  161 
Venter,  189 
Vernation,  166 
Vesicles,  259 
Viability,  237 

Water,  150 
Water,  ascent  of,  103 
Water,  conduction  of,  103 
Water,  current  of,  276 
Water-plants,  133 
Wax,  56 
Whorl,  170 
Winter  rest,  203 
Woody  parenchyma,  73 

Xantophyll,  15 
Xerophilous,  150 
Xylem,  75 

Yew,  251 

Zea,  68,  85 
Zoogarnetes,  191 
Zygomorphic,  219 
Zygomycetes,  194 
Zygospore,  188 


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"        Higher  Linear  Perspective 8vo,  3  50 

' '        Linear  Perspective 12mo,  1  00 

"        Machine  Construction 2  vols.,  8vo,  7  50 

Plane  Problems , 12mo,  125 

' '        Primary  Geometry 12mo,  75 

"        Problems  and  Theorems 8vo,  2  50 

"        Projection  Drawing 12mo,  150 

"        Shades  and  Shadows 8vo,  3  00 

"        Stereotomy— Stone  Cutting 8vo,  250 

Whelpley's  Letter  Engraving 12mo,  2  00 

ELECTRICITY  AND  MAGNETISM. 

ILLUMINATION— BATTERIES — PHYSICS. 

Anthony  and  Bracken's  Text-book  of  Physics  (Magie).   . . .  8vo,  4  00 

Barker's  Deep-sea  Soundings 8vo,  2  00 

Benjamin's  Voltaic  Cell 8vo,  3  00 

Cosmic  Law  of  Thermal  Repulsion  18mo,  75 

Crehore  and  Squier's  Experiments  with  a  New  Polarizing  Photo- 
Chronograph ; 8vo,  3  00 

*  Dredge's  Electric  Illuminations. .  .  .2  vols.,  4to,  half  morocco,  25  00 

Vol.11 4to,  750 

Gilbert's  De  magnete.     (Mottelay .) 8vo,  2  50 

Holman's  Precision  of  Measurements 8vo,  2  00 

Michie's  Wave  Motion  Relating  to  Sound  and  Light, 8vo,  4  00 

Morgan's,  The  Theory  of  Solutions  and  its  Results 12mo,  1  00 

Niaudet's  Electric  Batteries.     (Fishback.) 12rno,  2  50 

Reagan's  Steam  and  Electrical  Locomotives 12mo  2  00 

Thurston's  Stationary  Steam  Engines  for  Electric  Lighting  Pur- 
poses  12mo,  1  50 

Tillman's  Heat 8vo,  1  50 

ENGINEERING. 

CIVIL— MECHANICAL— SANITARY,  ETC. 

(See  also  BRIDGES,  p.  4 ;  HYDRAULICS,  p.  8 ;  MATERIALS  OF  EN- 
GINEERING, p.  9  ;  MECHANICS  AND  MACHINERY,  p.  11  ;  STEAM  ENGINES 
AND  BOILERS,  p.  14.) 

Baker's  Masonry  Construction 8vo,  5  00 

Baker's  Surveying  Instruments. 12mo,  3  00 

Black's  U.  S.  Public  Works. 4to,  5  00 


Btitts's  Engineer's  Field-book 12mo,  morocco,  $2  50 

Byrne's  Highway  Construction 8vo,  7  50 

Carpenter's  Experimental  Engineering 8vo,  6  00 

Church's  Mechanics  of  Engineering — Solids  and  Fluids  —  8vo,  6  00 

"       Notes  and  Examples  in  Mechanics 8vo,  2  00 

Crandall's  Earthwork  Tables 8vo,  1  50 

Crandall's  The  Transition  Curve 12mo,  morocco,  1  50 

*  Dredge's  Penn.  Railroad  Construction,  etc.  . .  Folio,  half  mor.,  20  00 

*  Drinker's  Tunnelling 4to,  half  morocco,  25  00 

Eissler's  Explosives — Nitroglycerine  and  Dynamite 8vo,  4  00 

Gerhard's  Sanitary  House  Inspection .16mo,  1  00 

Godwin's  Railroad  Engineer's  Field-hook.  12mo,pocket-bk.  form,  2  50 

Gore's  Elements  of  Goodesy 8vo,  2  50 

Howard's  Transition  Curve  Field-book 12mo,  morocco  flap,  1  50 

Howe's  Retaining  Walls  (New  Edition.) 12mo,  1  25 

Hudson's  Excavation  Tables.    Vol.  II 8vo,  1  00 

Button's  Mechanical  Engineering  of  Power  Plants 8vo,  5  00 

Johnson's  Materials  of  Construction 8vo,  6  00 

Johnson's  Stadia  Reduction  Diagram.  .Sheet,  22£  X  28£  inches,  50 

"         Theory  and  Practice  of  Surveying 8vo,  4  00 

Kent's  Mechanical  Engineer's  Pocket-book 12mo,  morocco,  5  00 

Kiersted's  Sewage  Disposal 12mo,  1  25 

Kirkwood's  Lead  Pipe  for  Service  Pipe 8vo,  1  50 

Mahan's  Civil  Engineering.     (Wood.) 8vo,  500 

Merriman  and  Brook's  Handbook  for  Surveyors. . .  .12mo,  mor.,  2  00 

Merriman's  Geodetic  Surveying 8vo,  2  00 

"         Retaining  Walls  and  Masonry  Dams 8vo,  2  00 

Mosely's  Mechanical  Engineering.     (Mahan.) 8vo,  5  00 

Nagle's  Manual  for  Railroad  Engineers .12mo,  morocco, 

Patton's  Civil  Engineering ,8vo,  7  50 

"       Foundations 8vo,  500 

Rockwell's  Roads  and  Pavements  in  France 12mo,  1  25 

Ruif tier's  Non-tidal  Rivers  8vo,  1  25 

Searles's  Field  Engineering 12mo,  morocco  flaps,  3  00 

Searles's  Railroad  Spiral 12mo,  morocco  flaps,  1  50 

Siebert  and  Biggin's  Modern  Stone  Cutting  and  Masonry. .  .8vo,  1  50 

Smith's  Cable  Tramways 4to,  2  50 

Wire  Manufacture  and  Uses. .. 4to,  300 

7 


Spalding's  Roads  and  Pavements 12mo,  $2  00 

"         Hydraulic  Cement i....l2ino,  200 

Thurston's  Materials  of  Construction  8vo,  5  00 

*  Trautwiue's  Civil  Engineer's  Pocket-book.  ..12mo,  mor.  flaps,  5  00 

*  "           Cross-section Sheet,  25 

*  "           Excavations  and  Embankments 8vo,  2  00 

"           Laying  Out  Curves 12mo,  morocco,  2  50 

Wait's  Engineering  and  Architectural  Jurisprudence. 

(In  the  press.} 

Warren's  Stereotomy— Stone  Cutting 8vo,  2  50 

Webb's  Engineering  Instruments .12mo,  morocco,  1  00 

Wegmanu's  Construction  of  Masonry  Dams 4to,  5  00 

Wellington's  Location  of  Railways 8vo,  5  00 

Wheeler's  Civil  Engineering 8vo,  4  00 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 

HYDRAULICS. 

WATER-WHEELS — WINDMILLS — SERVICE  PIPE — DRAINAGE,  ETC. 

(See  also  ENGINEERING,  p.  6.) 
Bazin's  Experiments  upon  the  Contraction  of  the  Liquid  Vein 

(Trautwine) 8vo,  2  00 

Bovey  's  Treatise  on  Hydraulics 8vo,  4  00 

Coffin's  Graphical  Solution  of  Hydraulic  Problems 12mo,  2  50 

Ferre!' s  Treatise  on  the  Winds,  Cyclones,  and  Tornadoes. .  .8vo,  4  00 

Fuerte's  Water  and  Public  Health 12mo,  1  50 

Oanguillet  &  Kutter'sFlow  of  Water.  (Heriug&  Trautwine  ).8vo,  4  00 

Hazeu's  Filtration  of  Public  Water  Supply 8vo,  2  00 

Herschel's  115  Experiments 8vo,  2  00 

Kiersted's  Sewage  Disposal 12mo,  1  25 

Kirkwood's  Lead  Pipe  for  Service  Pipe 8vo,  1  50 

31fisou's  Water  Supply 8vo,  5  00 

Merrimau's  Treatise  on  Hydraulics. . 8vo,  4  00 

Nichols's  Water  Supply  (Chemical  and  Sanitary) 8vo,  2  50 

Ruffner's  Improvement  for  Non-tidal  Rivers 8vo,  1  25 

Wegmaun's  Water  Supply  of  the  City  of  New  York 4to,  10  00 

Weisbach's  Hydraulics.     (Du  Bois.) 8vo,  5  00 

Wilson's  Irrigation  Engineering 8vo,  4  00 

Wolff's  Windmill  as  a  Prime  Mover 8vo,  3  00 

Wood's  Theory  of  Turbines 8vo,  2  50 

8' 


MANUFACTURES. 

ANILINE — BOILERS— EXPLOSIVES— IRON— SUGAR — WATCHES- 
WOOLLENS,  ETC. 

Allen's  Tables  for  Iron  Analysis 8vo,  $3  00 

Beaumont's  Woollen  and  Worsted  Manufacture 12ino,  1  50 

Bollaud's  Encyclopaedia  of  Founding  Terms 12mo,  3  00 

The  Iron  Founder 12mo,  250 

Supplement 12mo,  250 

Booth's  Clock  and  Watch  Maker's  Manual 12mo,  2  00 

Bouvier's  Handbook  on  Oil  Painting 12mo,  2  00 

Eissler's  Explosives,  Nitroglycerine  and  Dynamite 8vo,  4  00 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,  1  00 

Metcalfe's  Cost  of  Manufactures 8vo,  5  00 

Metcalf 's  Steel— A  Manual  for  Steel  Users 12mo,  2  00 

Keimaun's  Aniline  Colors.     (Crookes.) 8vo,  2  50 

*  Reisig's  Guide  to  Piece  Dyeing 8vo,  25  00 

Spencer's  Sugar  Manufacturer's  Handbook 12mo,  inor.  flap,  2  00 

"        Handbook  for  Chemists  of  Beet  Houses.  (In  the  press.} 

Svedelius's  Handbook  for  Charcoal  Burners 12mo,  1  50 

The  Lathe  and  Its  Uses 8vo,  6  00 

Thurston's  Manual  of  Steam  Boilers 8vo,  5  00 

Walke's  Lectures  on  Explosives 8vo,  4  00 

West's  American  Foundry  Practice 12mo,  2  50 

"      Moulder's  Text-book  12mo,  2  50 

Wiechmaun's  Sugar  Analysis 8vo,  2  50 

Woodbury's  Fire  Protection  of  Mills 8vo,  2  50 

MATERIALS  OF  ENGINEERING. 

STRENGTH — ELASTICITY — RESISTANCE,  ETC. 
(See  also  ENGINEERING,  p.  6.) 

Baker's  Masonry  Construction. 8vo,  5  00 

Beardslee  and  Kent's  Strength  of  Wrought  Iron  8vo,  1  50 

Bovey's  Strength  of  Materials 8vo,  7  50 

Burr's  Elasticity  and  Resistance  of  Materials 8vo,  5  00 

Byrne's  Highway  Construction 8vo,  5  00 

Carpenter's  Testing  Machines  and  Methods  of  Testing  Materials 

Church's  Mechanic's  of  Engineering — Solids  and  Fluids 8vo,  6  00 

Du  Bois's  Stresses  in  Framed  Structures 4to,  10  00 


Halfield's  Transverse  Strains 8vo,  $5  00 

Johnson's  Materials  of  Construction 8vo,  6  00 

Lanza's  Applied  Mechanics.    8vo,  7  50 

"        Strength  of  Wooden  Columns 8vo,  paper,  50 

Merrill's  Stones  for  Building  and  Decoration 8vo,  5  00 

Merritnan's  Mechanics  of  Materials  8vo,  4  00 

Pattou's  Treatise  on  Foundations 8vo,  5  00 

Rockwell's  Roads  and  Pavements  in  France 12mo,  1  25 

Spaldiug's  Roads  and  Pavements 12mo,  2  00 

Thurston's  Materials  of  Construction 8vo,  5  00 

Thurston's  Materials  of  Engineering 3  vols.,  8vo,  8  00 

Vol.  I.,  Non -metallic 8vo,  200 

Vol.  II.,  Iron  and  Steel... 8vo,  3  50 

Vol.  III.,  Alloys,  Brasses,  and  Bronzes 8vo,  2  50 

Weyrauch's  Strength  of  Iron  and  Steel.    (Du  Bois.) 8vo,  1  50 

Wood's  Resistance  of  Materials 8vo,  2  00 

MATHEMATICS. 

CALCULUS— GEOMETRY— TRIGONOMETRY,  ETC. 

Baker's  Elliptic  Functions 8vo,  1  50 

Ballard's  Pyramid  Problem   8vo,  1  50 

Barnard's  Pyramid  Problem 8vo,  1  50 

Bass's  Differential  Calculus 12mo,  4  00 

Brigg's  Plane  Analytical  Geometry 12mo,  1  00 

Chapman's  Theory  of  Equations 12mo,  1  50 

Chessin's  Elements  of  the  Theory  of  Functions 

Cora p toil's  Logarithmic  Computations 12rno,  1  50 

Craig's  Linear  Differential  Equations 8vo,  5  00 

Davis's  Introduction  to  the  Logic  of  Algebra 8vo,  1  50 

Halsted's  Elements  of  Geometry ...8vo,  175- 

"       Synthetic  Geometry 8vo,  150 

Johnson's  Curve  Tracing 12mo,  1  00 

"        Differential  Equations— Ordinary  and  Partial 8vo,  350 

"        Integral  Calculus 12mo,  1  50' 

"        Least  Squares 12mo,  1  50 

Ludlow's  Logarithmic  and  Other  Tables.     (Bass.) 8vo,  2  00 

Trigonometry  with  Tables.     (Bass.) 8vo,  3  00 

Mahan's  Descriptive  Geometry  (Stone  Cutting) .8vo,  1  50 

10 


Merriman  and  Woodward's  Higher  Mathematics 8vo,  $5  00 

Merriinau's  Method  of  Least  Squares 8vo,  2  00 

Parker's  Quadrature  of  the  Circle 8vo,  2  50 

Rice  and  Johnson's  Differential  and  Integral  Calculus, 

2  vols.  in  1,  12mo,  2  50 

"                  Differential  Calculus 8vo,  350 

"                  Abridgment  of  Differential  Calculus 8vo,  1  50 

Searles's  Elements  of  Geometry 8vo,  1  50 

Totten's  Metrology 8vo,  2  50 

Warren's  Descriptive  Geometry 2  vols.,  8vo,  3  50 

' '        Drafting  Instruments 12mo,  1  25 

"        Free-hand  Drawing 12mo,  100 

"        Higher  Linear  Perspective 8vo,  350 

"        Linear  Perspective 12mo,  1  00 

"        Primary  Geometry 12mo,  75 

Plane  Problems 12mo,  125 

"        Plane  Problems 12mo,  125 

"        Problems  and  Theorems 8vo,  2  50 

"        Projection  Drawing 12mo,  150 

Wood's  Co-ordinate  Geometry 8vo,  2  00 

"       Trigonometry 12mo,  1  00 

Woolf 's  Descriptive  Geometry. Royal  8vo,  3  00 

MECHANICS-MACHINERY. 

TEXT-BOOKS  AND  PRACTICAL  WORKS. 
(See  also  ENGINEERING,  p.  6.) 

Baldwin's  Steam  Heating  for  Buildings... 12mo,  2  50 

Benjamin's  Wrinkles  and  Recipes 12mo,  2  00 

Carpenter's  Testing  Machines  and   Methods  of   Testing 

Materials Svo, 

Chordal's  Letters  to  Mechanics 12mo,  2  00 

Church's  Mechanics  of  Engineering Svo,  6  00 

"        Notes  and  Examples  in  Mechanics Svo,  2  00 

Crehore's  Mechanics  of  the  Girder Svo,  5  00 

Cromwell's  Belts  and  Pulleys 12mo,  1  50 

Toothed  Gearing 12mo,  150 

Compton's  First  Lessons  in  Metal  Working 12mo,  1  50 

Dana's  Elementary  Mechanics 12mo,  1  50 

11 


Dingey's  Machinery  Pattern  Making 12mo,  $2  00 

Dredge's     Trans.     Exhibits     Building,      World     Exposition, 

4to,  half  morocco,  15  00 

Du  Bois's  Mechanics.     Vol.  I.,  Kinematics 8vo,  3  50 

"               Vol.11.,   Statics 8vo,  400 

Vol.  III.,  Kinetics 8vo,  350 

Fitzgerald's  Boston  Machinist. ...  .18mo,  1  00 

leather's  Dynamometers 12mo,  2  00 

Rope  Driving 12mo,  200 

Hall's  Car  Lubrication 12mo,  1  00 

Holly's  Saw  Filing 18mo,  75 

Lanza's  Applied  Mechanics 8vo,  7  50 

MacCord's  Kinematics 8vo,  5  00 

Merriman's  Mechanics  of  Materials 8vo,  4  00 

Metcalfe's  Cost  of  Manufactures 8vo,  5  00 

Michie's  Analytical  Mechanics 8vo,  4  00 

Mosely's  Mechanical  Engineering.     (Mahau.) 8vo,  5  00 

Richards's  Compressed  Air 12mo,  1  50 

Robinson's  Principles  of  Mechanism 8vo,  3  00 

Smith's  Press- working  of  Metals 8vo,  Ji  00 

The  Lathe  and  Its  Uses 8vo,  6  00 

Thurstou's  Friction  and  Lost  Work 8vo,  3  00 

The  Animal  as  a  Machine 12mo,  1  00 

Warren's  Machine  Construction 2  vols.,  8vo,  7  50 

Weisbach's  Hydraulics  and  Hydraulic  Motors.    (Du  Bois.)..8vo,  5  00 
"          Mechanics    of   Engineering.      Vol.    III.,    Part   I., 

Sec.  I.     (Klein.) 8vo,  500 

Weisbach's   Mechanics    of  Engineering.     Vol.    III.,    Part   I., 

Sec.II.     (Klein.) 8vo,  500 

Weisbach's  Steam  Engines.     (Du  Bois.) , 8vo,  500 

Wood's  Analytical  Mechanics 8vo,  3  00 

"      Elementary  Mechanics 12mo,  125 

"               "                  "           Supplement  and  Key 125 

METALLURGY. 

IRON— GOLD— SILVER — ALLOYS,  ETC. 

Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Egleston's  Gold  and  Mercury 8vo,  7  50 

12 


Egleston's  Metallurgy  of  Silver 8vo,  $750 

*  Kerl's  Metallurgy — Copper  and  Iron 8vo,  15  00 

*  "                Steel,  Fuel,  etc 8vo,  1500 

Kunbardt's  Ore  Dressing  in  Europe 8vo,  1  50 

Metcalf  Steel— A  Manual  for  Steel  Users 12mo,  2  00 

O'Driseoll's  Treatment  of  Gold  Ores 8vo,  2  00 

Thurstou's  Iron  and  Steel 8vo,  3  50 

Alloys 8vo,  250 

Wilson's  Cyanide  Processes 12mo,  1  50 

MINERALOGY   AND   MINING. 

MINE  ACCIDENTS — VENTILATION— ORE  DRESSING,  ETC. 

Barriuger's  Minerals  of  Commercial  Value (In  the  pref8.) 

Beard's  Ventilation  of  Mines 12mo,  2  50 

Boyd's  Resources  of  South  Western  Virginia 8vo,  3  00 

Map  of  South  Western  Virginia Pocket-book  form,  2  00 

Brush  and  Pen  field's  Determinative  Mineralogy 8vo,  3  50 

Chester's  Catalogue  of  Minerals 8vo,  1  25 

"       Dictionary  of  the  Names  of  Minerals.. 8vo,  3  00 

Dana's  American  Localities  of  Minerals 8vo,  1  00 

"      Descriptive  Mineralogy.     (E.  S.) 8vo,  half  morocco,  12  50 

Mineralogy  and  Petrography.     (J.  D.) 12mo,  2  00 

"      Minerals  and  How  to  Study  Them.     (E.  S.) 12mo,  1  50 

"      Text-book  of  Mineralogy.    (E.  S.) 8vo,  3  50 

*Drinker's  Tunnelling,  Explosives,  Compounds,  and  Rock  Drills. 

4to,  half  morocco,  25  00 

Egleston's  Catalogue  of  Minerals  and  Synonyms 8vo,  2  50 

Eissler's  Explosives — Nitroglycerine  and  Dynamite 8vo,  4  00 

Goodyear's  Coal  Mines  of  the  Western  Coast. 12mo,  2  50 

Hussak's  Rock  forming  Minerals.     (Smith.) 8vo,  2  00 

Ihlseng's  Manual  of  Mining 8vo,  400 

Kunhardt's  Ore  Dressing  in  Europe , 8vo,  1  50 

O'DHscoll's  Treatment  of  Gold  Ores 8vo,  2  00 

Rosenbusch's    Microscopical    Physiography   of    Minerals    and 

Rocks.     (Iddings.) 8vo,  500 

Sawyer's  Accidents  in  Mines 8vo,  7  00 

StDckbridge's  Rocks  and  Soils 8vo,  2  50 

13 


Williams's  Lithology 8vo,  $3  00 

Wilson's  Mine  Ventilation 16mo,  125 

STEAM  AND  ELECTRICAL  ENGINES,  BOILERS,  Etc. 

STATIONAKY — MARINE— LOCOMOTIVE — GAS  ENGINES,  ETC. 
(See  also  ENGINEERING,  p.  6.) 

Baldwin's  Steam  Heating  for  Buildings 12mo,  2  50 

Clerk's  Gas  Engine t 12mo,  400 

Ford's  Boiler  Making  for  Boiler  Makers 18mo,  1  00 

Heraenway 's  Indicator  Practice 1 2mo,  2  00 

Hoadley's  Warm-blast  Furnace 8vo,  1  50 

Knenss's  Practice  and  Theory  of  the  Injector 8vo,  1  50 

MacCord's  Slide  Valve 8vo, 

*  Maw's  Marine  Engines Folio,  half  morocco,  18  00 

Meyer's  Modern  Locomotive  Construction 4to,  10  00 

Peabody  and  Miller's  Steam  Boilers .8vo,  4  00 

Peabody's  Tables  of  Saturated  Steam 8vo,  1  00 

Thermodynamics  of  the  Steam  Engine 8vo,  5  00 

"          Valve  Gears  for  the  Steam-Engine 8vo,  2  50 

Pray's  Twenty  Years  with  the  Indicator Royal  8vo,  2  50 

Pupin  and  Osterberg's  Thermodynamics 12nio,  1  25 

Reagan's  Steam  and  Electrical  Locomotives. . . 12mo,  2  00 

Routgeu's  Thermodynamics.     (Du  B.ois.) 8vo,  5  00 

Sinclair's  Locomotive  Running 12mo,  2  00 

Thurston's  Boiler  Explosion 12mo,  1  50 

"           Engine  and  Boiler  Trials 8vo,  500 

Manual  of  the  Steam  Engine.      Part  I.,  Structure 

and  Theory  8vo,  7  50 

Manual  of  the   Steam  Engine.      Part  II.,    Design, 

Construction,  and  Operation 8vo,  7  50 

2  parts,  12  00 

"           Philosophy  of  the  Steam  Engine 12rno,  75 

Reflection  on  the  Motive  Power  of  Heat.    (Caruot.) 

12mo,  2  00 

"           Stationary  Steam  Engines 12mo,  1  50 

Steam-boiler  Construction  and  Operation 8vo,  5  00 

Spangler's  Valve  Gears 8vo,  2  50 

14 


Trowbridge's  Stationary  Steam  Engines 4to,  boards,  $2  50 

Weisbach's  Steam  Engine.     (Du  Bois.) 8vo,  500 

Whltbain'a  Constructive  Steam  Engineering 8vo,  10  00 

Steam-engine  Design 8vo,  6  00 

Wilson's  Steam  Boilers.     (Flather.) 12mo,  2  50 

Wood's  Thermodynamics,  Heat  Motors,  etc 8vo,  4  00 

TABLES,  WEIGHTS,  AND  MEASURES. 

FOR  ACTUARIES,  CHEMISTS,  ENGINEERS,  MECHANICS— METRIC 
TABLES,  ETC. 

Adriauce's  Laboratory  Calculations 12mo,  1  25 

Allen's  Tables  for  Iron  Analysis 8vo,  3  00 

Bixby's  Graphical  Computing  Tables Sheet,  25 

Compton's  Logarithms 12mo,  1  50 

Crandall's  Railway  and  Earthwork  Tables 8vo,  1  50 

Eglestou's  Weights  and  Measures 18mo,  75 

Fisher's  Table  of  Cubic  Yards Cardboard,  25 

Hudson's  Excavation  Tables.     Vol.  II 8vo,  1  00 

Johnson's  Stadia  and  Earthwork  Tables 8vo,  1  25 

Ludlow's  Logarithmic  and  Other  Tables.     (Bass.)  . . . 12mo,  2  00 

Thurston's  Conversion  Tables ...  8vo,  1  00 

Totteu's  Metrology 8vo,  2  50 

VENTILATION. 

STEAM  HEATING— HOUSE  INSPECTION— MINE  VENTILATION. 

Baldwin's  Steam  Heating. 12mo,  2  50 

Beard's  Ventilation  of  Mines 12mo,  2  50 

Carpenter's  Heating  and.  Ventilating  of  Buildings 8vo,  3  00 

Gerhard's  Sanitary  House  Inspection Square  16ino,  1  00 

Mott's  The  Air  We  Breathe,  and  Ventilation 16rno,  1  00 

Reid's  Ventilation  of  American  Dwellings 12mo,  1  50 

Wilson's  Mine  Ventilation 16mo,  1  25 

niSCELLANEOUS  PUBLICATIONS. 

Alcott's  Gems,  Sentiment,  Language Gilt  edges,  5  00 

Bailey's  The  New  Tale  of  a  Tub 8vo,  75 

Ballard's  Solution  of  the  Pyramid  Problem 8vo,  1  50 

Barnard's  The  Metrological  System  of  the  Great  Pyramid.  .8vo,  1  50 

15 


Davis'  Elements  of. Law 8vo,  $2  00 

Emmoti's  Geological  Guide-book  of  the  Rocky  Mountains.  .8vo,  1  50 

Fen-el's  Treatise  on  the  Winds 8vo,  4  00 

Haines'  Addresses  Delivered  before  the  Am.  Ry.  Assn. 

12mo.     (In  the  press.) 

Mott's  The  Fallacy  of  the  Present  Theory  of  Sound . .  Sq.  IGnio,  1  00 

Perkins's  Cornell  University Oblong  4to,  1  50 

Ricketts's  History  of  Rensselaer  Polytechnic  Institute 8vo,  3  00 

Rotherham's    The     New    Testament     Critically    Emphasized. 

12mo,  1  50 

Totteu's  An  Important  Question  in  Metrology 8vo,  2  50 

Whitehouse's  Lake  Moeris Paper,  25 

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